Family & Community Medicine Lecture Notes 2023 PDF

Family and Community Medicine Lecture Notes Book 2023 2022-2023  2 Family and Community Medicine| University of Benghazi | 2022-2023 ...

Family and Community Medicine Lecture Notes Book 2023 2022-2023  2 Family and Community Medicine| University of Benghazi | 2022-2023  3 Forward It is indeed privilege to introduce this book on behalf of family and community medicine department to the fourth year medical students. Though it is a huge responsibility and I hope to do justice. Family and community medicine department is meant basically with preventive medicine, the first defence line of any healthcare system. It deals with identification of risk factors to avoid occurrence of diseases, and what it is even better is to eliminated these risk factors. Thus health promotion will be achieved. It is well known that efficient health system indicators are healthy people at lower cost. These two indicators are the main concern of Family and Community Medicine speciality. Family and Community Medicine is a comprehensive field includes various specialities that cover epidemiology, biostatistics, research, communicable diseases, non-communicable diseases, environmental and occupational medicine, family medicine, demography, social and behavioural medicine. This book was collected with hope to meet the student`s academic needs in this field as an undergraduate. Best regards Amal A. Elfakhri Head of Family and Community Medicine department University of Benghazi [email protected] July 2022 Family and Community Medicine| University of Benghazi | 2022-2023  4 Table of Contents: Topic Staff Introduction to community medicine Prof. Azza A. Griew Epidemiology Prof. Tunis M. Meidan Prof. Amina A. Alshekteria Research proposal Dr. Mahmoud Alwerfalli Communicable diseases. Prof. Ahmed A. Towier Respiratory infections. Prof. Ekram A. Barakat Gastro-intestinal infections. Dr. Asma Borwis Zoonotic diseases. Dr. Monira Najem Descriptive Statistics Dr. Amal Elfakhri Inferential Statistics Dr. Alsanusi Taher Demography Dr.Fatma Y. Ziuo Non-communicable diseases Prof. Azza A. Griew Dr. Mahmoud Alwerfalli Dr. Essam Denna Family Medicine and Sociology Prof. Fatma S. Benkhaial Dr. Fatma Y. Ziuo Dr. Amenh Bilkasem Yousif Nutrition in health and disease Prof. Lubna J. Abdolmalek Dr. Saleh A. Elfaidi Environmental health Dr. Nadia A. Aldarogi Occupational health Prof. Ibrahim A. Alghaweel Dr.Saleh A. Elfaidi Dr. Essam Denna Health administration and Health Prof. Amina A. Alshekteria Care Quality Family and Community Medicine| University of Benghazi | 2022-2023  5 SECTION I: INTRODUCTION TO COMMUNITY MEDICINE Definition of Public Health Public health is the science and art of preventing disease, prolonging life and promoting health and efficiency through organized community effort for; Public Health is defined as the process of mobilizing local, state, national and international resources to solve the major health problems affecting communities and to achieve Health for All by 2000 by: a. The sanitation of the environment, b. Control of communicable diseases, c. Education of the individual in personal hygiene, d. Medical and nursing services for early diagnosis, e. To ensure adequate living standard of everyone for the maintenance of health. Therefore, Public Health: Is the combination of sciences, skills, and beliefs directed toward maintenance and improvement of health of all people through collective or social actions. Community Medicine:Is the science that concerns with the promotion of health, prevention, control, and management of diseases, disabilities, and other health problems in the community. It is the branch of medicine that is concerned with the community or a group of population rather than individual patients. Another definition of Community Medicine: It is the field that is concentrated on the study of health and disease in the population of defined community or a group of population. In short, Community Medicine provides comprehensive health services ranging from preventive, promotive, curative to rehabilitative services. Goals of Community Medicine: 1- To identify the health problems and needs of a defined population. 2- To plan, implement, and evaluate the extent to which health measures effectively meet these needs. Clinical Medicine Clinical medicine is one type of scientific medicine that gives more emphasis on practice and is using basic science oriented e.g. Chemistry, biology, microbiology and pharmacology. It deals with patients in which a physician diagnosis the disease of a patient and prescribes medicine and keeps the patient in follow-up care. Its main objectives are: Removal of disease from patient rather than from a group of population and treatment of disease by the use of many types of medications. CONCEPTS OF HEALTH Concept means general idea and hence concepts are pillars of our understanding. Health is fundamental right of an individual. Definition:As per World Health Organization (WHO) in 1948: "Health is a state of complete physical, mental and social wellbeing and not merely an absence of disease or infirmity ".In recent years, “Ability to lead a socially and economically productive life” has also been taken into consideration. Family and Community Medicine| University of Benghazi | 2022-2023  6 The definition of WHO in 1998 was further improved by adding two important items; dynamic and spiritual: “Health is a dynamic state of complete physical, mental, spiritual and social, well-being and not merely the absence of disease or infirmity. (WHO; 1998)  Dimensions of health:Health is multidimensional. WHO definition of health includes 4 dimensions; physical, mental, spiritual and social. Many dimensions may be mentioned as emotional, vocational and political.  Holistic Concept of health; It has been defined as unified or multidimensional process involving the wellbeing of the whole person in the context of his environment. All sectors of society have an effect on health 1. Physical dimension:Physical health is a state in which every cell and every organ is functioning at optimum capacity and in perfect harmony with the rest of the body. The signs of physical health in an individual are good complexion, clean skin, eyes, sound sleep, regular activity of bowels and bladder, all special senses are intact, the resting pulse rate and blood pressure are within the range of normality. 2. Mental dimension:It is essential component of health, and has been defined as" a state of balance and harmony between the individual and surrounding world". Mentally healthy person is: - 1- Free of internal conflicts, 2- Not at war with himself, 3- Well with others, 4- He knows himself, his needs, problems and goals, 5- He has self-control, 6- He faces his problems and tries to solve them. 3. Social dimension:Social wellbeing implies harmony and integration between each individual and other members of society. It is the ability of the individual of building and maintaining satisfying relationships. 4. Spiritual dimension:It refers to our personal beliefs, values, principles and ethics. 5. Emotional dimension:Is ability to accept and cope with our own and others feelings. Mental health can be seen as "knowing" or "cognition" while emotional health relates to "feelings". 6. Vocational dimension: When work is fully adapted to human goals, capacities and limitations, work often plays a role in promoting both physical and mental health. Physical Work is usually associated with an improvement in physical capacity, while goal achievement and self – realization in work are a source of satisfaction and enhanced self – esteem. 7. Others:Other dimensions such as educational dimension, nutritional dimension, environmental dimension, cultural etc. play an important role in achieving the health. Positive health: It is the perfect functioning of the body and mind, It conceptualizes health biologically,as a state in which every cell and organ is functioning at optimum capacity and in perfect harmony with the rest of the body, psychologically, as a state in which the individual feels a sense of well – being Family and Community Medicine| University of Benghazi | 2022-2023  7 and of mastery over his environment, and socially, as a state in which the individual's capacities for participation in social system are optimal. Concept of well – being:The psychologists have pointed out that it has objective and subjective components. The objective component relates to term "standard of living" or "level of living " The subjective component of well – being is referred to as "quality of life." Standard of living: It includes the level of education, employment status, food, dress, house, level of provision of health and recreational services. These may be used as measures of socio economic status. Quality of life: Quality of life was defined by WHO as " the condition of life resulting from the combination of the effects of the complete range of factors such as those determining health, happiness, education, social and intellectual attainments, freedom of justice and action", quality of life is individual's own subjective evaluation of the standard of living factors, quality of life can be evaluated by assessing a person's subjective feelings of happiness or unhappiness about various life concerns. Physical quality of life Index (PQLI): It consolidates three indicators i.e. Infant mortality, life expectancy at age one, and literacy. Each component has a scale of 0-100 where 0 indicate worst and 100 indicate best performance. Spectrum of health: Health and disease lie along a continuum, and there is no single cutoff point. The lowest point on the health --disease spectrum is death and the highest point corresponds to WHO definition of positive health https://www.google.com.ly/imgres?imgurl=https%3A%2F%2Fimage.slidesharecdn. The spectral concept of health emphasizes that the health of an individual is not static. It is a dynamic phenomenon and a process of continuous change. Determinants of health: Health is an outcome of many factors (determinants); some of them are discussed below: 1. Biological/ Hereditary. 2. Environmental. 3. Socio – economic conditions Family and Community Medicine| University of Benghazi | 2022-2023  8 4. Life style 5. Health and family welfare services. 6. Others. 1. Biological / Hereditary: The physical and mental traits of an individual are to some extent determined by the genetic makeup and cannot be altered after conception. A number of diseases are now known to be of genetic origin e.g. chromosomal anomalies, errors of metabolism, mental retardation etc. 2. Environment:It can be divided into physical and psychosocial component; these are completely linked with one another. Environment can be also classified as micro- environment and macro – environment. o Micro-environment or domestic environment, e.g. eating habits, smoking, and use of drugs, etc. o Macro-environment or external environment, e.g. Air, water supply, housing, etc. 3. Social & economic conditions:Health status is determined primarily by their level of socio – economic status which includes: a. Economic status:It is usually measured by per capita income; the economic status determines the purchasing power, standard of living, quality of life, family size and pattern of disease in community. As poverty / effluence may also be a contributory factor of illness such as coronary heart disease, diabetes etc. b. Education:A second major factor influencing health status is education especially female education. The world map of illiteracy closely coincides with the maps of poverty, malnutrition, ill health, high infant and child mortality. c. Occupation:Unemployment can lead to higher incidence of ill health and death. 4. Life style:It means "the way people live" reflecting a whole range of social values, attitudes and activities. It is composed of cultural and behavioral patterns and lifelong personal habits (e.g. Smoking, alcoholism, etc.) 5. Health & Family Welfare services:Health services cover a wide spectrum of personal and community services for treatment of disease, prevention of illness and promotion of health for example; immunization, provision of safe water, care of pregnant women & children. 6. Other factors: These are factors that affect the health of the population and are outside the formal health care system e.g. food and agriculture, education, industry, employment opportunities, family support system, etc. CONCEPT OF DISEASE It is the state of deviation from normal health. The distinction between illness, sickness, and disease is as follows- Family and Community Medicine| University of Benghazi | 2022-2023  9 Disease:is an objective state of physiological / psychological dysfunction. Illness:is a subjective state of the person who feels aware of not being well. Sickness:is a state of social dysfunction (role). Concept of causation:Causation means that there is a true mechanism that leads from exposure to disease. Cause:It is an event or condition that plays a role in the occurrence of a disease. Germ theory of disease:In this theory microbes were considered the sole cause of disease. This gives one to one relationship between causal agent and disease, and the disease. It is now recognized that a disease is rarely caused by a single agent alone but many other factors contribute to its occurrence. Epidemiological triad model The occurrence of the disease in exposed host needs other factors relating to the host and environment. This model consists of; Host, Agent and Environment and have been used for many years. It helped the epidemiologists to focus on different classes of factors, especially with regard to infectious diseases. https://essenceofhumanbeing.wordpress.com/current-medical-model-analysis. Agents Host factors Environmental factors Family and Community Medicine| University of Benghazi | 2022-2023  10 Biological agents: Demographic Physical environment living agents of characteristics Non – living things such as air , diseases: suchas age, sex andethnicity water , viruses, rickettsiae, etc. soil , housing climate, fungi, bacteria etc. light , heat, noise , radiation etc. Nutrient agents: Biological:e.g., genetic, Biological environment – Protein, fat, carbohydrate, biochemical living things – microbial agents, vitamins, minerals and blood groups, enzymes. insects, rodents, animals water. & plants. Chemical agents: Psychosocialenvironment ; Endogenous: e.g. urea, Socio economic: cultural values, customs, habits, serum bilirubin, ketones education, beliefs, attitudes, morals, Exogenous: e.g. allergens, occupation, stress, religion, education, metals, acids, alkalis, gases marital status etc. health services etc. Mechanical agents chronic friction and other Life style factors Living mechanical habits, nutrition, etc. forces etc. Social agents: poverty, smoking, drug & alcohol abuse Multi factorial causation and web of causation: New types of diseases were discovered e.g. cancer, heart disease, mental illnesses which could not be explained on the basis of germ theory, known as chronic / non communicable diseases, result from interaction of many factors as social, economic, cultural, genetic and psychological factors. Family and Community Medicine| University of Benghazi | 2022-2023  11 Natural history of disease: Is the way in which a disease evolves over time from the earliest stage of its pre-pathogenesis phase to its termination. It consists of three phases: 1- Pre – pathogenesis, the period before onset of disease(i.e. the process in the environment). The agent has not yet entered man) 2- Pathogenesis(i.e. the process in humans). 3- Termination phase: The disease usually results in terms of: - Recovery or Death or Disability. Levels of prevention and the natural history of disease. (Redrawn from Leavell, H. F., & Clark, E. G. 1965. Preventive medicine for the doctor in his community: An epidemiologic approach. New York: McGraw- Hill.) Risk Factors and risk groups Risk factor (RF): It is an aspect of personal behavior or life-style, an environmental exposure, or an inborn or inherited characteristic, which on the basis of epidemiologic evidence, is known to be associated with health related conditions. Family and Community Medicine| University of Benghazi | 2022-2023  12 Risk Factors can be “modifiable”such as smoking, hypertension, elevated serum cholesterol, physical inactivity, and obesity, or “non-modifiable“ such as age, sex, race, family history, and genetic factors. Risk factors may be characteristic of the individual, family, group orcommunity. Individual risk factors include age, sex, smoking, etc. Community risk factors such as presence of malaria, air pollution, poor water supply, poor health care services, etc. Examples of some of the Risk factors and associated diseases or conditions: Disease Risk Factors Heart disease Smoking, high blood pressure, elevated serum cholesterol, diabetes, obesity, lack of exercise and type A personality. Cancer Smoking, alcohol, solar radiation, work – site hazards and dietary factors. Stroke High blood pressure, smoking and elevated serum cholesterol. Accidents Alcohol, non – use of seat belts, speed, Motor vehicle and improper road way design Risk groups (Vulnerable groups): Certain population is at risk to have more morbidity and mortality and WHO promotes to identify Risk groups or target groups e.g. at risk mothers, at risk infants, at risk families, handicapped, elderly etc. in the population by defined criteria. Spectrum of disease: The term "spectrum of disease" is a graphic representation of variations in the manifestations of disease. At one end of the disease spectrum are sub-clinical Infections which are not ordinarily identified and at the other end are fatal illnesses and in the middle of the spectrum are the illnesses ranging in severity from mild to severe. The spectrum of disease in infectious disease is also referred to as the "gradient of infection" Iceberg Phenomenon of disease: According to this concept, disease in a community may be compared with iceberg. The tip of iceberg represents what the physicians see in the community i.e. clinical cases, and the vast submerged portion of the iceberg represents the hidden mass of the disease, i.e. latent, in- apparent, pre–symptomatic, undiagnosed cases and carriers in the community. In some diseases (e.g. hypertension, diabetes, anemia, malnutrition, mental illness), the unknown morbidity (i.e. the submerged portion of the iceberg), far exceeds the known morbidity. The hidden part of the iceberg constitutes an important, undiagnosed reservoir of infections or diseases in community. Its detection & control is a very important technique in preventive medicine. Family and Community Medicine| University of Benghazi | 2022-2023  13 CONCEPT OF CONTROL Concept of control describes ongoing operations aimed at reducing: (i) The incidence of disease (ii) The duration of disease, and consequently the risk of transmission. (iii) The effects of infection including both the physical and psychosocial complications. (iv) The financial burden on the community. Disease control:In disease control, "agent" is permitted to persist in the community at a level where it ceases to be a public health problem according to the tolerance of the local population. Disease elimination: The term elimination is used to describe interruption of disease transmission from large geographic regions. It is an important precursor for eradication. e.g. Measles, Polio. Elimination is an intermediate goal between control and eradication. Disease eradication: Eradication of disease implies termination of all transmission of infection by extermination of the infectious agent. In other words, eradication is cessation of infection and disease from the whole world. The only disease that has been eradicated is smallpox, in 1980. Recently, three diseases have been advanced as candidates for global eradication within foreseeable future: polio, measles and dracunculosis. Family and Community Medicine| University of Benghazi | 2022-2023  14 Monitoring:It is “the performance and analysis of routine measurement aimed at detecting changes in the environment or health status of population” e. g. Water monitoring, air pollution monitoring, growth and nutritional status monitoring, etc. Surveillance:It is defined as “the continuous scrutiny of the factors that determine the occurrence and distribution of disease and other conditions of ill-health”. It is a method of identification of all cases, susceptible contacts, those who are at risk. Objectives of surveillance: 1. To provide information about new and changing trends in the health status of a population, e.g. morbidity, mortality, nutritional status etc. 2. To provide feedback to all concerned personnel for adequate and timely action. 3. To provide timely warning of public health disasters so that interventions can be initiated. Evaluation: It is process by which results are compared with the stated objectives, or more simply the assessment of how well a program is performing. Evaluation can be done in mid-way or at the end of program. CONCEPT OF PREVENTION Prevention: According to Last dictionary of public health is defined as actions focused on eliminating or minimizing the impact of disease and disability, or delaying the progress of disease and disability.The goal of prevention is to stop the progression of a disease or prevent it from occurring. There are four stages of prevention. Family and Community Medicine| University of Benghazi | 2022-2023  15 (1) Primordial prevention: '' it is the prevention of the emergence, establishment or development of the social, economic and cultural patterns of living that are known to contribute to an elevated risk of diseases in countries or population groups in which they have not yet appeared." Example: Discouraging children from adopting harmful lifestyles e.g. lack of exercise, eating unhealthy food, smoking etc. to reduce obesity, hypertension etc. Most primordial actions occur at the population level rather than at the individual level (e.g., sanitation, establishing healthy communities, and economic reforms) (2) Primary prevention: It is undertaken at the pre-pathogenesis phase by modifying or eliminating the risk factors of disease. It prevents the onset of disease by changing health behaviors, reducing risk factors or enhancing the body’s resistance to diseases. Primary prevention actions can occur at both the population and individual level (e.g., seat-belt legislation, most vaccinations). It is undertaken by a) Health promotion. b) Specific promotion. a) Health promotion: Health promotion is "the process of enabling people to increase control over, and to improve health." It is intended to strengthen the host by: i) Health education, ii) Environmental modification iii) Nutritional interventions and iv) Lifestyle and behavioral changes. b) Specific protection: 1- Immunization e.g. Vaccine preventable diseases. 2- Specific nutrient e.g. Iron. 3-Protection against injuries (helmet, seat belt) 4-Chemoprophylaxis e.g. against Malaria. 5-Control of consumer product quality and safety of foods, drugs, cosmetics, etc. Approaches for primary prevention: WHO has recommended the following approaches for the primary prevention of chronic diseases: a) Population (mass strategy), b) High – risk strategy. (3) Secondary prevention: It prevents the establishment or progression of a disease once a person has been exposed to it and provision of adequate treatment (e.g., screening mammography program, which detects breast cancer at an early stage when intervention may be more cost-effective). Most secondary prevention actions occur on an individual level (4) Tertiary prevention: It can be defined as "all measures available to reduce or limit impairments and disabilities, minimize suffering caused by existing departures from good health and it aims to decrease the impact of the disease through better physician and individual management (e.g., cardiac rehabilitation after a heart attack). All tertiary prevention actions occur at an individual level. It is undertaken through Disability limitation and Rehabilitation. a) Disability limitation: The sequence of events leading to disability and handicap is as follows: Disease e.g. car crash➔Impairment e.g. loss of foot ➔Disability e.g. cannot walk & will be unemployed Family and Community Medicine| University of Benghazi | 2022-2023  16 b) Rehabilitation It is the combined and coordinated use of medical, social, educational and vocational measures for training and retraining the individual to the highest level of functional ability. Types of rehabilitation: a) Medical – restoration of function. b) Vocational - restoration of the capacity to earn a livelihood. c) Social - restoration of family and social relationships. d) Psychological rehabilitation - restoration of personal dignity and confidence. (5) Quaternary prevention: It is defined as “action taken to identify patient at risk of over medicalization, to protect him from new medical invasion, and to suggest him interventions that are ethically acceptable.” It makes it easier to “identify patient at risk of over-medicalization.” It depends on the concept of “first, do no harm.” ____________________________________________________________________________ INDICATORS OF HEALTH Indicators:These are variables which help to measure changes. An Ideal Indicator is 1. Valid 2. Reliable & objective 3. Sensitive 4. Specific 5. Feasible 6. Relevant The indicators of health may be classified as: Sr. Types of Measurement tools no. indicators 1. Mortality Crude death rate, Expectation of life, Infant mortality rate, indicators Child mortality rate, Under-Five proportional mortality rate, Maternal mortality rate, Disease specific mortality rate, Proportional Mortality rate etc. 2. Morbidity Incidence and prevalence, Notification rates, Attendance rates at OPD indicators Admission and discharge rates, Duration of stay in hospital, etc. 3. Disability Event type – no. of days of restricted activity, indicators Bed disability days, work loss days , Person type – Limitation of mobility and activity Sullivan’s index, Disability Adjusted Life Years (DALY), 4. Nutritional Anthropometric measurement, Prevalence of low birth weight status indicators 5. Health care Doctor – population ratio, Doctor – Nurse ratio, Population- bed ratio. delivery indicators. 6. Utilization Immunization coverage, Bed – occupancy rate &Bed turnover ratio indicators 7. Socio Literacy rate, Family size, Per capita GNP, Per capita "calorie" availability economic indicators Family and Community Medicine| University of Benghazi | 2022-2023  17 Health status indicators: Low birth weight (percentage). Nutritional status and psychosocial development of children. Infant mortality rate (1- 4 years). Life expectancy at birth. Maternal mortality rate. Disease specific mortality rate. Morbidity – incidence and prevalence. Disability prevalence. Millennium Development Goals (MDGs): The origin of the Millennium Development Goals (MDGs) is to be found in the United Nations’ Millennium Declaration that was adopted on 8 September 2000 by all of the 189 member states (147 of which were represented by their heads of State or Government). These goals were set for the year 2015 with reference to the international situation prevalent in 1990. The Following are MDGs: Goal 1: Eradicate extreme poverty & hunger Goal 2: Achieve universal primary education Goal 3: Promote gender equality & empower women Goal 4: Reduce child mortality Goal 5: improve maternal health Goal 6: Combat HIV/AIDS, TB, malaria & other diseases Goal 7: Ensure environmental sustainability Goal 8: Develop global partnership for development Family and Community Medicine| University of Benghazi | 2022-2023  18 SURVEILLANCE According to World Health Organization surveillanceis defined as; “Systematic ongoing collection, collation, and analysis of data and the timely dissemination of information to those who need to know so that the action can be taken” The main elements in surveillance are: 1. Collection of health data 2. Ongoing collection of data 3. Timely analysis 4. Easily understood 5. Dissemination of results 6. Action based on results 7. Periodic evaluation of the system Uses of surveillance systems: A- To monitor changes or trends in health factors such as: i- Prevalence/incidence of disease and/or risk factors ii- Emerging diseases iii- Geographic distribution iv- Risk group distribution B- To detect outbreaks/early warning systems related to; i- Human disease ii- Zoonotic diseases; e.g., SARS, H5N1 iii- Food safety iv- Drug-resistant organisms (e.g., MDR-TB) C- To provide health information that can be used to design rational intervention programs D- To evaluate the effectiveness of intervention strategies (e.g., vaccines, health education/behavioral programs, legislation) Requirements for surveillance a- Diagnostic system b- Staff members c- Sampling frame d- Access/network e- Competent laboratory Surveillance systems should start by: A- Defining a case by using; a- Establishing a functional case criteria: this step should be quickly and easily defined b- Selecting the right test or definition: this should be made easy and specific c- Disease versus infection: i.e., AIDS and HIV infection Family and Community Medicine| University of Benghazi | 2022-2023  19 B- Selecting the population: There should be selection criteria of the population , whether it will be human populations or zoonotic populations and also it is important to know the access used to reach to target populations for example non-governmental organizations or support groups. After selecting the population their cooperation should be obtained and maintained C- Selecting the appropriate surveillance type: There are different strategies to be selected. Thus, the surveillance team should understand the effects and limitations of different types D- Sources of Surveillance Data: There are many sources of surveillance data available. vital records, such as birth certificates, and death certificates. Environmental monitoring systems, animal health data, information provided from individuals, information from laboratories, medical records at outpatient healthcare facilities, as well as hospitals. Over the counter medication sales can be a source of data. Registries are sources of data, and finally surveys. Some examples of surveys are population-based surveys such as stepwise survey E- Analysis: By using the analysis of the collected data, any changes in the prevalence of infection, disease or risk activities and there will be establishment of trends, new reservoirs & new foci (groups/locations) F- Timely data processing: After analysis of the data the results should be interpreted and accordingly appropriate actions should be applied. G- Evaluation and revisions It is of great importance to keep an ongoing evaluation system and to revise the surveillance program. Types of Surveillance: There are mainly three types; Active, passive and sentinel surveillance 1- Active: This type occurs when the collection of data from the lab, physician, or other healthcare provider is initiated by the health department. Active surveillance is often used during outbreak investigations or research studies. An active surveillance system provides stimulus to health care workers in the form of individual feedback or other incentives. Often reporting frequency by individual health workers is monitored; health workers who consistently fail to report or complete the forms incorrectly are provided specific feedback to improve their performance. There may also be incentives provided for complete reporting. Active surveillance has an advantage over passive surveillance because it achieves more complete and accurate reporting. However, the disadvantage Family and Community Medicine| University of Benghazi | 2022-2023  20 is that it requires more resources. It costs more, it takes more personnel, and more time to do active surveillance.. It is often used if an outbreak has begun or is suspected to keep close track of the number of cases. Community health workers may be asked to do active case finding in the community in order to detect those patients who may not come to health facilities for treatment. 2- Passive: Reports are coming from different sources as; hospitals, laboratories, clinics &physicians. Passive surveillance means that the healthcare provider or laboratory initiates the forwarding of the data to the health department. Health authorities do not stimulate reporting by reminding health care workers to report disease nor providing feedback to individual health workers. Passive surveillance is the most common type of surveillance in humanitarian emergencies. Most surveillance for communicable diseases is passive. The surveillance coordinator may provide training to health workers in how to complete the surveillance forms, and may even send someone to periodically collect forms from health facilities. But little attention is given to individual health workers who report the information. The data requested of each health worker is minimal. Nonetheless, passive surveillance is often incomplete because there are few incentives for health workers to report. 3- Sentinel surveillance:Instead of attempting to gather surveillance data from all health care workers, a sentinel surveillance system selects, either randomly or intentionally, a small group of health workers from whom to gather data. These health workers then receive greater attention from health authorities than would be possible with universal surveillance. Sentinel surveillance also requires more time and resources, but can often produce more detailed data on cases of illness because the health care workers have agreed to participate and may receive incentives. It may be the best type of surveillance if more intensive investigation of each case is necessary to collect the necessary data. For example, sentinel poliomyelitis surveillance in Libya previously by detailed case history from suspected cases and stool specimen collection for detection of virus under recommended conditions. Collection of such data from all health workers would not be possible. The sentinel groups includes; i-High-risk individuals & vulnerable individuals ii-Exposed individuals (e.g., health workers) The sentinel sites includes; i-Previous reports of high prevalence ii-Areas where there is exposure to high-risk individuals iii- Residence areas of suspected concentration of high-risk groups iv-Residence of susceptible/vulnerable groups v-Cross-border regions Importance of sentinel surveillance: 1. Early warning of epidemic: e.g. HIV incidence/prevalence in high-risk groups. Presence of HIV infection in high-risk groups warns local people that unless control measures are taken, HIV infection will soon spread throughout the general community 2. Identification of size and scope of epidemic Family and Community Medicine| University of Benghazi | 2022-2023  21 e.g. Identification of size and scope of HIV epidemic such as; estimating HIV prevalence in high- and low-risk groups, by time and geographic region. Once the magnitude of the HIV epidemic is recognized, political leaders will be able to unite the people in their efforts to control the disease 3. Short-term evaluation of control efforts e.g. Short-term evaluation of HIV/AIDS control efforts. This will be reflected as follows: - Change in prevalence - Change in risk factors (i.e. in high- and low-risk groups) - After the HIV control program is underway, the surveillance system is used to measure changes in factors leading to infection 4. Long-term evaluation of control efforts e.g. Long-term evaluation of HIV/AIDS control efforts - HIV incidence in high- and low-risk Groups. After many years, the surveillance system will be able to evaluate if control programs have reduced the size and scope of the HIV epidemic- Incidence and prevalence in high- and low-risk groups 5. Stimulate decision makers and social action e.g. Information on HIV puts pressure on decision makers to provide additional resources for stimulating action in the community Evaluation of a surveillance system The surveillance system can be evaluated by assessing the following: 1- Sensitivity: To evaluate the sensitivity of surveillance system by measuring the proportion of identified cases and detect whether the system give an accurate picture of trends and magnitude. 2- Timeliness: To estimate the time duration taken for dissemination of information was enough to permit timely action based on the surveillance system. 3- Representativeness: To detect the difference between reported and unreported cases. 4- Acceptability: To find out the effect of the system on stimulating the cooperation of respondents or it discourage participation. 5- Flexibility: Can changes be easily made in the system to reflect changes in trends, magnitude, and other relevant factors. 6- Simplicity: To detect when the system is simplified it will still obtain the necessary information 7- Cost/benefit: To find out that the system worth the cost or not and also if costs could be reduced without sacrificing the essential quality of the system. 8- Dissemination of results: Results should be distributed to decision-makers, to data collectors, and to the general public. 9- Appropriate action taken: To estimate if appropriate actions were taken in response to the surveillance data and if there was an effective intervention after surveillance. SECTION II: PRINCIPLES OF EPIDEMIOLOGY Family and Community Medicine| University of Benghazi | 2022-2023  22 Definition: “The study of the distribution and determinants of health-related states or events in specified population and the application of this study to the control of health problems” 1. Distribution: It is to study pattern of distribution of diseases or health events or states in the various groups / subgroups of population in terms of person, place and time by asking Who (persons), is affected more by a disease or who remain free from it within a population. Where (place) a health related event has occurred When, (time) such event has occurred or existed. 2. Determinants: Include both causes and factors that influence the risk of disease. They are grouped under epidemiological triad as-agent factors, host factors and environmental factors. Aims of epidemiology: 1. To describe the distribution and size of disease problems in human populations 2. To identify aetiological factors in the pathogenesis of disease 3. To provide the data essential to the planning, implementation and evaluation of services for the prevention, control and treatment of disease and to the setting up of priorities among those services The ultimate aim of epidemiology is to lead to effective action 1-To eliminate or reduce the health problem or its consequences. 2-To promote the health and well-being of society as A whole. Epidemiological approach: The epidemiological approach of health and disease is based on two major foundations: Family and Community Medicine| University of Benghazi | 2022-2023  23 1. Asking questions 2. Making comparison 1 - Asking questions: Learning or asking questions and getting answers that lead to further questions. For example, the following questions could be asked. a. Related to health events: -What is the event? (The problem) -When did it happen? - What is its magnitude? -Who are affected? – Where did it happen? - Why did it happen? b. Related to health action: – What can be done to reduce this problem sector? Where and for whom these activities and its consequences? be carried out? –How can it be prevented in the future? – What resources are required? How are the activities to be organized? – What action should be taken by the community? By the health services? By other –What difficulties may arise, and how might they be overcome? Answer to the above questions may provide clues to disease aetiology, and help the epidemiologist to guide planning and evaluation. 2 - Making comparisons: Comparison of two or more groups; in which one group having the disease and the other group not having the disease. We should ensure comparability between study and control groups. It means comparing like with like Family and Community Medicine| University of Benghazi | 2022-2023  24 USES OF EPIDEMIOLOGY 1. Historical study: Is the community improving? We can decide only by comparing experience (rates) over time, because it is well known that the health and disease pattern in communities never constant. There are fluctuations both over short and long periods of time. Example: old disease small pox, new ones legionnaires’ disease, Lassa fever, AIDS. 2. Community diagnosis: What are the health problems? Community diagnosis generally refers to the identification and quantification of health problems in a community in terms of mortality and morbidity rates and ratios. By quantification of health problems, we lay down priorities in disease control and prevention. The quantification of health problems can be a source of new knowledge about distributions, and prevention. 3. Planning and evaluation: Planning is essential for rational use of the limited resources. Epidemiological information about the distribution of health problems over time and place provides the fundamental basis for planning and developing the needed health services and for assessing the impact of these services on the people's problems. Any measures taken to control or prevent a disease must be followed by an evaluation 4. Evaluation of individual’s risks and chances: It measures degree of risks in the population. Measures of absolute risk (incidence & specific rates), relative risk and attributable risk for a factor related to or believed to be a cause of the disease. Example: the risk of bearing a Mongol child, the risk of some hereditary disorders, etc. 5. Syndrome Identification:The epidemiological investigation can be used to define and refine the rising number of syndromes. 6. Completing the natural history of disease: The epidemiologist by studying disease patterns in the community in relation to agent, host and environmental factors is in a better position to fill up the gaps in the natural history of disease than the clinician who sees only an episode in the natural history of disease. 7. Searching for causes and risk factors: The search for causes is the most obvious use of epidemiology. Most hypothesis-testing studies have primary aim of identifying causal factors or at least risk factors for disease.The contributions of epidemiology have been many in this regard. Example: - Rubella is the cause of congenital defects in the new-born. - Thalidomide is a teratogenic agent - Cigarette smoking is a causal factors of lung cancer - Exposure of premature babies to oxygen is the cause of retrolental fibroplasia. Family and Community Medicine| University of Benghazi | 2022-2023  25 TOOLS OF MEASUREMENT IN EPIDEMIOLOGY There are three basic tools to measure the frequency of disease, health related states and events: A. Rates B. Ratios and C. Proportions. A. RATES: A rate measures the occurrence of a particular even or state (heart rate, disease, death, disability, health needs, health care utilization etc.) in a population during a given period of time. Time is usually a calendar year (one year from 1 st of January –31st December). The rate is expressed (usually) per 1000 or some other round figure (10,000,100.000) selected to avoid fractions. Numerator is a part of denominator. Types of rates: i) Crude rates: (un-standardized rates) actual observed frequency of an event is expressed in terms of rates e.g. Crude Birth Rate, Crude Death Rate etc. ii) Specific rates: Observed frequency is expressed in terms of rate due to: 1. Specific cause (T.B, typhoid) 2. Specific sex (male, female) 3. Specific age (under five years, 5-15 years, 15-45 years), 4. Specific time period (annual, monthly, weekly). ii) Standardized rates: These rates are obtained by direct or indirect method of standardization or adjustment by age, sex, and called as age and sex standardize rates B. RATIO: Dividing the frequency of one event, characteristic, part by the, frequency of another event, characteristic, parts e.g. male- female ratio, doctor- population ratio, child - women ratio In a Ratio, numerator is NOT a part of denominator and No multiplier is used C. PROPORTION: Proportion is the relation of frequency of one part to the frequency of the whole (total). Proportions are expressed as a percentage (proportions multiplied by 100). Example: Number of under- nourished children at a certain time Proportion= ------------------------------------------------------------------------ x 100 Total number of children in an area at the same time Family and Community Medicine| University of Benghazi | 2022-2023  26 MEASURES OF MORBIDITY Morbidity is defined as “Any departure, subjective or objective, from a state of physiological well-being”. It includes sickness, illness, disability. There are two measures of morbidity: 1-Incidence rate: Incidence rate (I.R) measures the occurrence of NEW cases of the health problem under study in a specific population during a specified period of time. Types of incidence rate: A. Cumulative incidence rate (Risk). B. Attack rate. C. Secondary attack rate (SAR) Each type is used in different situation to measure the occurrence of new cases. A. Incidence rate: It is a measure of NEW cases of the health problem under study. It is the number of unaffected individuals who on an average contract (get) the disease under study in a specified period of time (usually one year). Number of NEW cases of a disease under study during a specified period of time Incidence rate = ____________________________________________ x 1000 Total susceptible population or population at risk of developing the disease under study during a specified period of time. B. Attack rate: It measures the frequency of new cases when the population is exposed to an agent for a limited period of time, such as during an epidemic. It measures the extent or magnitude of the disease during an epidemic. Attack rate = Number of cases of the disease during an epidemic period X 100 Total people at risk of developing the disease during the same epidemic period C. Secondary Attack Rate (SAR): It is the number of exposed susceptible persons developing the disease within the range of one incubation period following exposure to Family and Community Medicine| University of Benghazi | 2022-2023  27 the primary case.SAR is estimated for infectious diseases (measles, influenza) in which primary case is infectiveonly for a short period of time. It also measures the communicability of a disease. Number of exposed susceptible persons developing the disease within the range of one incubation period SAR =________________________________________________x100 Total number of exposed susceptible contacts Uses of SAR: i. To measure the spread or communicability of an infection within family or in a closed group e.g. hostel inmates ii. To know the communicability of a new disease iii. To evaluate the control and preventive measures. Examples:vaccination, isolation, etc. 2-Prevalence Rate (PR):Prevalence Rate (PR) measures the total number of cases (NEW + OLD) present in a specified population at a given point of time. Types of prevalence rate: (a) Point prevalence rate.(b) Period prevalence (a) Point prevalence rate: It is defined as the total number of all cases (NEW + OLD) of a disease in a specified population, at A GIVEN POINT OF TIME. The given point might be of one day, several days, few weeks depending upon the time survey takes to examine /interview /enumerate (count) Number of all cases (old + new) of a disease under study, Point prevalence = existing at a given point of time in a specified population x 100 or 1000 Estimated population(examined/interviewed) at the same point in time When the term “prevalence rate” is used, without any further qualification, it means “point prevalence rate” only. (b) Period Prevalence Rate: This is not used frequently. It measures the total number of cases (NEW AND OLD) existing during A DEFINED PERIOD OF TIME(e.g. annual prevalence, monthly prevalence etc.). Family and Community Medicine| University of Benghazi | 2022-2023  28 Number of all cases (old+new) of a disease existing during Period prevalence rate = a given period of time in a specified population x 100 or 1000 Estimated population (examined/interviewed) during the same period Relationship between prevalence and Incidence: Prevalence rate of a disease depends on two factors that is Incidence rate of a disease and Duration of a disease. If the population is stable, incidence rate and duration of a disease relationship is expressed as- Prevalence = Incidence rate (I) x Duration of disease (D) or P = I x D Uses of incidence and prevalence rates: Family and Community Medicine| University of Benghazi | 2022-2023  29 Incidence rate Prevalence rate - To plan control and preventive measures - To estimate the total magnitude of a disease in the - To evaluate control & preventive measures i.e. community if incidence rate of a disease is increasing after- To identify potential high risk population application of control and preventive - Useful for administrative and planning purposes measures, it indicates failure of the measures. - To plan facilities to deal with the total magnitude There is a need for new measures or present of disease e.g. Number of beds, doctors, nurses, measures needs modification required drugs, rehabilitation facilities. - Provides research direction in to a disease MEASURES OF MORTALITY Measures of Mortality A wide variety of rates, ratios and proportions have been developed to measure death/ mortality. Purposes of measuring mortality: 1- To understand the trends in mortality of 5- To monitor the any health program. a community 6- Mortality measures provide clue 2- To explain changes in the overall to epidemiology mortality 3- To decide priorities for health action, to 7- Measure of health of the community. allocate resources. 4- To evaluate the measures which are applied to reduce the mortality Commonly used Mortality Measures: 1. Crude Death Rate(CDR) 4. Case Fatality Rate (CFR) 2. Specific death rate (age, sex, cause) 5. Standardized rates. 3. Proportional mortality rates. 6. Survival rate 1. Crude death rate (CDR):it is Number of deaths (from ALL causes, ALL age groups, BOTH sexes) in one year, in a given place per 1000 mid -year population Mid-year population: means the population on 1st July of that year Crude death rate = No. of deaths during the yearX 1000 Family and Community Medicine| University of Benghazi | 2022-2023  30 Mid - year population 2. Specific death rate: a) Age specific death rates e.g. Children below 5 years b) Sex specific death rates e.g. male, female c) Cause specific death rates e.g. TB, Diabetes and cancer. Specific death rates Formula a-Specific death rate for males Number of deaths among males during a calendar year x 1000 Mid- year population of male b-Specific death rate in the age Number of deaths of persons in the age group group of 15 to 45 years 15-45 yrs during a calendar year x 1000 Mid –year population of persons in the age group 15-45 yrs. c-Specific death rate for Number of deaths from T.B during a calendar year x 1000 Tuberculosis (T.B.) Mid-year population d-Specific death rate for breast Number of deaths from breast cancer x 1000 cancer (female) Mid- year population of females above the age of 30 yrs. 3. Proportional mortality rates: These rates are used when population data is not available. It is useful to know what proportion of deaths have occurred in a particular age group, sex or due to specific cause (cancer, Road traffic accidents, heart disease etc.). Proportional mortality from specific disease Age-specific proportional mortality Sex specific proportional mortality Family and Community Medicine| University of Benghazi | 2022-2023  31 In estimating proportional mortality, denominator is total number of deaths. Proportional mortality is expressed as a percentage by multiplying with 100. Proportional mortality rates Formula a-Proportional mortality from a specific Number of deaths from cancer x 100 disease e.g. Cancer Total deaths from all causes in the same year b-Under-five children proportional Number of deaths among mortality rate under five children in the year x 100 Total number of deaths at all ages during the same year c-Proportional mortality for females Number of deaths among females in a given year x 100 Total number of deaths in both sexes 4. Case Fatality Rate (CFR): It is referred to as “the number of deaths among persons diagnosed with a disease(patients). Case fatality rate is used in acute infectious diseases (food poisoning, cholera, and measles). Case fatality is expressed in percentage. It represents the “killing power” of a disease. Total number of deaths due to a particular disease CFR = ---------------------------------------------------------- x 100 Total number of cases of the same disease 5. Standardized Death Rates: Comparison of death rates of two populations with different age compositions should be done by age adjustment or age standardization as Crude Death rate cannot provide correct comparison. This removes the confounding effect of different age structures. There are two methods: Family and Community Medicine| University of Benghazi | 2022-2023  32 a) Direct standardization This method is feasible only if the actual specific rates in subgroups of the observed population are available along with the number of individuals in each subgroup. b) Indirect standardization: Most commonly used method is Standardized Mortality Ratio (SMR). It is a ratio of the total number of deaths that occur in the study group to the number of deaths that would have been expected to occur if study group experienced death rate of the standard population. SMR = Observed deaths ÷ Expected deaths × 100 6. Survival Rate: It is the proportion of survivors in a group studied and followed over a period (usually 5 years). It is a method of describing prognosis in certain disease conditions. Total number of patients alive after a specific period Survival rate = ------------------------------------------------------------------ x 100 Total number of patients diagnosed or treated Family and Community Medicine| University of Benghazi | 2022-2023  33 INVESTIGATION OF AN EPIDEMIC Epidemic means the unusual occurrence of a disease or specific health related behaviours (like smoking) or other health related events (accident) clearly in excess of expected occurrence The occurrence of an epidemic indicates that there are changes have taken place in the existing balance of agent, host and environment. This change may be due to: - Recent increase in multiplication of the - Enhanced mode of transmission, increase agent, in the exposure of host, - Recent increase in infectivity / virulence - Change in the susceptibility of the host & of the agent, response to the agent and - Recent introduction of the new agent, - Introduction through new portals of entry. Objectives of an investigation: a) To bring current epidemic under d) To identify the specific factors and immediate control situations responsible for occurrence b) To estimate the magnitude of of an epidemic epidemic disease (attack rates, case e) To identify source/s of infection & fatality rate) mode of transmission to apply c) To describe the epidemic disease in appropriate measures to check relation to Time, Place, and Person further transmission f) To give recommendations to prevent similar epidemic in future Steps of an epidemic investigation: 1. Verification of diagnosis of an epidemic 2. Confirmation of the existence of an epidemic. 3. Defining the population at risk 4. Rapid search for all cases from the community and their characteristics 5. Data analysis in terms of Time, Place & Person distribution of epidemic. 6. Formulation of hypothesis on probable cause/s of an epidemic 7. Testing of hypothesis 8. Evaluation of ecological factors 9. Further investigation of population at risk 10. Writing a report Family and Community Medicine| University of Benghazi | 2022-2023  34 1-Verification of diagnosis: Verification of diagnosis of epidemic disease should be done quickly, by clinical examination and laboratory investigation on few cases, if diagnosis has not already been established. However, epidemic investigation should not be delayed until the diagnosis is verified, if existence of an epidemic is confirmed. 2- Confirmation of the existence of an epidemic: First step is to confirm whether epidemic exists or not. An epidemic is said to exist when the number of cases are in excess of the expected frequency for the specified population during the same period in previous years. Epidemics of cholera, food poisoning, Hepatitis A, conjunctivitis are easily recognized. While epidemics of diabetes,TB, Hypertension, Cardiovascular diseases are not easily recognized unless the present frequency is compared with the same period of previous year(month to month comparison) 3. Defining the population at risk: (Obtain information on population and area)Information on total population (at risk population), its age & sex distribution is required to estimate the age and sex specific attack rates. Area wise map should have important landmarks like school, hospital, factory and water storage tank. This may help in relating the occurrence of cases to the place of residence, place of occupation or education. Family and Community Medicine| University of Benghazi | 2022-2023  35 4. Rapid search for all cases and their characteristics: A house to house medical survey in defined area to identify all cases including those who have not visited hospital and to estimate the magnitude of epidemic disease is needed. If community is very large, random sample may be chosen. Data on cases need to be collected daily on Epidemiological Case Sheet (ECS) from community, hospital, health centres& private doctors. Epidemiological case sheet is an important tool to investigate an epidemic. It includes name ,age ,sex occupation of person, history of recent travel , special events such as attended party, history of common exposure to water , milk ,blood transfusion, infection, time of onset of first signs and symptoms. These sheets ensure uniformity of data collection. Search for new cases to be carried out daily till the area is declared free of an epidemic i.e. twice the incubation period of the disease after the last case or death occurs (epidemic disease). Family and Community Medicine| University of Benghazi | 2022-2023  36 5. Analysis of data: Data should be analysed by person, place and time factors a. Person factors:All factors related to person like age, sex, occupation, socio-economic status, exposure to risk factors etc. should be studied. Age and sex specific attack rates must be estimated. If needed food specific, occupation specific, habit specific etc. attack rates may be estimated depending on the type of epidemic disease. b. Place: Place or area specific attack rate can be estimated if area wise population is known. This can provide powerful evidence about the differences related to host or environmental factors. Every day, area wise cases/deaths should be entered in the map by dots (Dot-map or Spot –map). If area-wise population is not available, dot map will give clue on high or low frequency of disease in an area. This can be judged by looking at clustering of cases on the dot map/ area map. c. Time: Analysis of data by time is routinely presented in the form of an epidemic curve. Number of cases are shown on Y – axis (vertical) and Time on X-axis (horizontal). It should be done in terms of Time relationship -whether common or propagated source or seasonal/cyclic pattern. Spot –map cases Family and Community Medicine| University of Benghazi | 2022-2023  37 6. Formulation of hypothesis: Hypothesis is a tentative explanation for the cause(s) of an epidemic. It is developed in the light of time, place and person distribution, analysis, inference and report of the ecological survey. Many times more than one hypothesis is formulated to explain the possible source of infection,, mode of spread and environmental factors which led to an epidemic. Control and preventive measures may be possible to apply at this stage. 7. Testing of hypothesis: Hypothesis is tested by comparing attack rates among exposed and non-exposed e.g. comparing the attack rates of an area which was supplied with contaminated water supply and area with safe water supply. 8-Evaluation of ecological survey: Investigating teams carry out community survey and inspect water source, sewage system, milk supply system, food establishment, check for air pollution, sudden changes in weather, deaths of animals, breeding places for vectors, and movement of human population etc. This is to identify: The circumstances responsible for the epidemic, Source(s) of infection and Mode(s) of transmission of infection to plan & apply immediate control measures. 9. Further investigation of population at risk: The study of the population at risk or a sample of population may be studied for additional information. This may involve medical examinations screening tests, examination of suspected food and water,biochemical investigations, immunity status etc. A case-control or cohort study can be done to find out the causes or factors or in- apparent illnesses etc. Family and Community Medicine| University of Benghazi | 2022-2023  38 10. Writing a report:A final report having detailed possible answers on how, why, where, who (suffers), when is prepared and submitted to the local health department by the investigating team. A copy of the report is also submitted to concerned hospital(s) and department of environment. A simple and precise report may be prepared for the community where the epidemic had occurred. Family and Community Medicine| University of Benghazi | 2022-2023  39 TYPES OF EPIDEMIOLOGICAL STUDIES The most common types of epidemiological studies are: Types of epidemiological studies Experimental Observational - Randomized Descriptive: controlled study Analytical: -Case report (clinical trial) -Case control -Case series - Field trial study - ecological -Community - Cohort study (co-relation) trial -Cross sectional A. OBSERVATIONAL STUDIES: Descriptive and analytical studies are observational studies, in which epidemiologist only observes the natural history of a disease or health related event without any active intervention or action or manipulation. 1. DESCRIPTIVE STUDIES: A descriptive study involves describing the characteristics of a particular situation, event or case. Descriptive studies can be carried out on a small or larger scale. It always describes the event in person, place and time. The descriptive study can answer the research question by asking what, when, where, who, and how for an event. These studies basically ask the questions: 1-Who is getting the disease? (Person distribution) 2- Where is it occurring? (Place distribution.) 3- When is the disease occurring? (Time distribution) Describing the disease in terms of person, place and time (Some characteristics): - PERSON DISTRIBUTION: Family and Community Medicine| University of Benghazi | 2022-2023  40 In this, investigator may use inherent characteristics of people (for example, age, race, sex), their acquired characteristics (immune or marital status), their activities (occupation, leisure activities, use of medications/tobacco/drugs), or the conditions under which they live (socioeconomic status, access to medical care). These categories determine to a large degree that is at greatest risk of experiencing some undesirable health condition, such as becoming infected with a particular disease organism. a. Age: Age is probably the single most important person’s attribute because almost every health-related event or state varies with age. Certain diseases are more frequent in certain age groups than others- e.g. Measles in childhood, Cancer in middle age, Atherosclerosis in old age etc. “Bimodality “means a particular disease is common at two age groups e.g. Hodgkin's disease, leukaemia and female breast cancer. b. Sex: Some diseases are more common in women than mene.g. chronic diseases such as hyperthyroidism & obesity and others in men such as lung cancer and coronary heart disease. This may be due to differences in life style and behavioural factors. c. Marital status: It has been found that mortality rates were lower for married males and females than unmarried of the same age and sex. Marital status may be the risk for some disease. d. Occupation: Occupation may alter the habits of employees e.g. sleep, alcohol, smoking, drug addiction, night shifts, etc. It is obvious that persons working in a particular occupation are exposed to particular types of risks e.g. workers in coalmines are more likely to suffer from silicosis, sedentary workers face the risk of heart disease, etc. e. Social class: Epidemiological studies have shown that health and disease are not equally distributed among social classes. Individuals in the upper social classes have longer life expectancy and better health and nutritional status than those in the lower social classes, certain diseases (e.g. CHD, hypertension, diabetes) have shown a higher prevalence in upper classes than in the lower classes. f. Life style: Risk factors in non-communicable diseases such as CHD, cancer, obesity and accidents are commonly due to change in behaviour e.g. cigarette smoking, sedentary life, over-eating and drug abuse. This leads to increase in the disease frequency. g. Ethnicity (Race):Differences observed in racial, ethnic, or other groups may be due to their susceptibility or exposure, or other factors that might have increased the risk of developing disease(s), such as socioeconomic status and access to health care. - PLACE DISTRIBUTION: Descriptive epidemiology related to place could provide major in-sight in disease aetiology. There may be differences in disease pattern from one place to another. The variations may be classified as: Family and Community Medicine| University of Benghazi | 2022-2023  41 i. International variations iii. Rural -urban differences ii. National variations iv. Local distribution i. International variations: Descriptive studies by place have shown that the pattern of disease is not the same everywhere. There is a marked difference between the incidence of each disease in different parts of the world e.g. cancer of stomach is common in Japan, but unusual in US. There are international variations in breast cancers, oesophageal cancers, cardiovascular diseases etc. ii. National variations: Disease frequency can be different between regions within the country. iii. Rural -urban differences: Variations in disease distribution are well known e.g. chronic bronchitis; accidents, lung cancer, cardio-vascular disease, mental illness and drug dependence are usually more frequent in urban areas than in rural areas. On the other hand, skin and Zoonotic diseases are more frequent in rural areas than in urban areas. Death rates especially infant and maternal mortality rates, are higher in rural than urban areas. These variations may be due to differences in population density, social class, level of education etc. iv. Local distribution: Inner and outer city variations in disease frequency are well known. These variations are best studied with the aid of “spot maps” or “Shaded maps "e.g. John Snow’s investigation of cholera. TIME DISTRIBUTION: The pattern of disease can be described by time of its occurrence according to day, week, month, or year. Time distribution will be able to describe increasing or decreasing trend, whether the disease is seasonal in occurrence, periodic increase or decrease or it follows consistent time trend. This helps to formulate the hypothesis. Epidemiologists have identified three kinds of time trends or fluctuations in disease occurrence. A. Short- term fluctuations or variations B. Periodic fluctuations or variations. C. Long term or secular trends or variations A. Short - term fluctuations: The best known short-term fluctuation in the occurrence of diseases is an epidemic, e.g.: Epidemic of food Poisoning. Various types of short-term fluctuations (epidemics) are as follows: a) Common source ii. Multiple exposure or i. Person to person. epidemic: continuous or persistent epidemic i. Single exposure or “point ii. Arthropod vector. source” epidemic b) Propagated epidemic. Family and Community Medicine| University of Benghazi | 2022-2023  42 iii. Animal reservoir. d) Slow (modern) epidemic. a) Common source epidemic: i. Single exposure or “point source” epidemic: e.g. Food poisoning The main features of a point source epidemic are- The epidemic curve rises and falls rapidly with no secondary waves. The epidemic tends to be explosive and there is clustering of cases in short interval of time All cases develop within one incubation period of a disease. ii. Multiple exposure or continuous or persistent epidemic: In these epidemics, the sources are common but exposure is prolonged and continuous, repeated or intermittent and not necessarily at the same time or place. The epidemic continues for more than one incubation period and there are no secondary cases. E.g. Contaminated well of water. b) Propagated epidemic: i. Person to person ii. Arthropod vector. iii. Animal reservoir Mostly infectious in origin usually results from person to person transmission, e.g. Hepatitis ‘A’, polio, etc. The epidemic shows a gradual rise and tails off over a much longer period of time. Family and Community Medicine| University of Benghazi | 2022-2023  43 Transmission continues until the number of susceptible has depleted or the susceptible persons are no longer in contact with the infected person. The speed of spread depends on the herd immunity (the capacity of the population to fight infection) of a community. This commonly occurs in the population who has large number of susceptible individuals to sustain infection. c. Slow epidemics:These are modern or slow epidemics of Chronic / non-communicable diseases (Diabetes, hypertension, cancers, etc). The time scale is shifted from days/weeks /months to years. B. Periodic fluctuations: 1. Seasonal trend 2. Cyclic trend 1. Seasonal variations: Number of cases varies in a particular season. For example: Measles and Chicken pox in spring season, gastrointestinal infection common in summer season and skin & respiratory tract infection common in winter season. The seasonal variation occurs due to change in environmental conditions like: temperature, humidity, rainfall, lack of sunlight, overcrowding, vector breeding etc. 2. Cyclic trend:Some diseases occur in cycles spread over a period of time (weeks, months, years).For example: Measles epidemic occurs every 6 – 7 years & rubella every 6 – 9 years. This is because of increases in number of susceptible individuals to such an extent that person to person transmission is possible which leads to epidemic. C. Long term or secular trends: The term secular trend implies changes in the occurrence of a disease over several years or decades. Examples - CHD, Lung cancer, and diabetes. Family and Community Medicine| University of Benghazi | 2022-2023  44 TYPES OF DESCRIPTIVE STUDIES: A. Observational descriptive studies: 1. Case Report Study: It is done for one case of unexpected outcome or previously unknown side effect of a drug Example:retrolental fibrosis of the retina and blindness of newly born when subjected to hyperbaric oxygen in NICU. 2. Case series Study: it is collection of case reports. It may indicate an impending epidemic of adisease. Example: cases of acute H1NI. “Both case report and case series are important to initiate a hypothesis to stimulate a new research but they are weak due to absence of comparison groups.” 3. Correlation studies(ecological): It uses data from entire populations to compare disease frequency between different groups during the same period of time or in the same population at different points in time.Example. correlation between number of cigarettes smoked per day and annual lung cancer deaths. Higher number of cigarettes smoked per day was related to increase in annual lung cancer deaths. It cannot estimate the individual's risk but helps in stimulating hypothesis for undertaking analytic studies. 4. Migration studies: Another useful technique in descriptive epidemiology is to study the effects of migration on the frequency of disease occurrence. These studies help clarify whether a disease of unknown cause is determined principally by genetic inheritance or by environmental exposure. Migration from a high-risk population to a low-risk population should not affect the occurrence of a genetically determined disease among the migrants. In contrast migration from a high-risk population to a low-risk population is expected to be associated with a reduction in occurrence of an environmentally determined disease. It means migration diminishes the likelihood of exposure to environmental risk factors, and accordingly the occurrence of disease. 5. Cross sectional surveys: Cross-sectional study is the simplest of all the observational studies. It is based on a single examination of a cross-section of population at one point in time. The results can be projected on the whole population provided the sampling has been done correctly. Cross-sectional study is also known as “prevalence study". Cross-sectional studies are more useful for chronic than acute diseases. Example: In a study of hypertension, we can collect data during the survey about age, sex, physical exercise, body weight, salt intake and other variables of interest. Such a study tells us about the distribution of a disease in population rather than its aetiology. Family and Community Medicine| University of Benghazi | 2022-2023  45 Steps in descriptive studies: 1. Defining the population to be studied. 4. Measurement of disease frequency. 2. Defining the diseases to be studied. 5. Comparing with known indices. 3. Describing the disease in term of Person, 6. Formulation of an aetiological hypothesis. Place and Time. Defining the population to be studied Defining the disease to be studied Describe the disease in terms of person, place and time Measurement of disease frequency Comparing with known results Formulation of an aetiological hypothesis Family and Community Medicine| University of Benghazi | 2022-2023  46 ANALYTICAL STUDIES It is the second major type of epidemiological studies. In contrast to descriptive studies that look at entire populations, in analytical studies, the subject of interest is the individuals within the population. The Objective is to test hypotheses. The evaluation is done in individual but the inference is applied to the population from which they are selected. Types of analytical studies: A. Case control study B. Cohort study A. CASE CONTROL (RETROSPECTIVE) STUDY It involves two populations - case and control. The unit of study is individual rather than group. It is a comparison study. The Objective is to test causal hypothesis. Features of case control study: i. Both exposure and outcome (disease) have occurred before the start of the study. ii. The study proceeds backwards from effect (disease or health related event) to cause. iii. It uses a control or comparison group to support or refute an inference. Diagram of a case-control Study Steps of case control study: 1. Selection of cases and controls 2. Matching 3. Measurement of exposure 4. Analysis and interpretation Family and Community Medicine| University of Benghazi | 2022-2023  47 1. Selection of cases and controls: i- Selection of case: there are many steps should be in consideration when selecting the cases a. Definition of a case: Cases should be newly diagnosed. Diagnostic criteria and histological type should be quite clear and not to be altered or changed till the study is over. b. Eligibility criteria: should be clear and set before selection of cases. Whether only new cases or old cases, diagnosed within a specified period of time are eligible or not, is to be decided. b. Sources of cases: - Hospitals: Cases may be selected from one or more hospitals, admitted during a specified periodof time. - General population: find out cases in the general population by a survey or from available records and select complete series of cases or sample of cases. By this method bias can be reduced, disease rate can be computed, but it needs more time & resources. It is not routinely done. ii. Selection of controls: Control should be free from the disease under study. Controls are essential to evaluate effect of exposure in causing a disease. They should be appropriate and similar to the cases as far as possible. a. Sources of controls: - Hospital controls: Can be selected from same hospital but admitted with condition other than the disease under study. e.g.: case of myocardial infarction (MI) from coronary care unit but controls from surgical or orthopaedic units (without MI). - Relatives: Family members or any other relatives who are not having the disease may be selected as controls. - Neighbourhood controls: selected from persons living in the same locality as cases e.g. persons working in the same factory or children attending the same school. - General population: controls can be obtained from defined geographical area by taking random sample of individuals free from disease under study. How many controls are needed? If the study is large, one control for each case. If the study group is small (less than 50 cases) then as many as 2, 3 or 4 for each case. It is desired to conduct more than one case control study in different geographic areas to increase the accuracy of the results. Family and Community Medicine| University of Benghazi | 2022-2023  48 II. Matching:it is defined as “the process by which we select controls in such a way that they are SIMILAR to cases with regard to certain variables, e.g. age & sex which are known to influence the outcome of the disease”; and which, if not adequately matched for comparability, could distort or confound the results. A ‘confounding factor’ is one which is associated with both exposure and disease, and not equally distributed in study and control groups, e.g. age of mother is related to both parity and birth weight of the child. III. Measurement of exposure: Definitions and criteria of exposure are very important. Information about exposure should be obtained in precisely the same manner both for cases and controls, by interviews, questionnaires or studying past records of cases (such as hospital records, employment records, school records, etc.) IV. Analysis: To find out: 1. Exposure rates among cases and controls to suspected factor. 2. Estimation of disease risk associated with exposure (odds ratio). FRAMEWORK OF CASE CONTROL STUDY Disease ( effect) Cause ( risk factor) Present Absent Present A (40) B (20) Absent C (60) D (80) Total a + c (100) b + d (100) a. Exposure rates: A case control study provides a direct estimation of the exposure rates to a suspected factor in disease and non- disease groups. From above example - Exposure rates among Cases = a/ (a + c) = 40 ÷100 x 100 = 40% Exposure rates among Controls= b/ (b + d) = 20 ÷100 x 100= 20% Family and Community Medicine| University of Benghazi | 2022-2023  49 b. Estimation of risk: Odds Ratio is a cross-product ratio. It is a measure of the strength of association between the risk factor and outcome. From above example - Odds Ratio= a × d÷ b × c = 40 x 80 ÷20 x 60 = 2.7, It means those mothers who are smoker have 2.7 times higher risk of having low birth weight babies than non - smoker mothers. Bias in case control studies: i. Selection bias: The person selecting the iv: Bias due to confounding control should not know the nature of the risk v. Berkesonian bias: This is due to different factor being studied. rates of admissions to hospital for people ii. Interviewer bias with different diseases (hospital cases and controls). iii. Recall bias Advantages of case control study: 1-Relatively easy to carry out 5-Several etiological factors can be studied 2-Rapid and inexpensive 6-No attrition problems 3-Suitable to investigate rare diseases 7-Ethical problems minimal. 4-No risks to subjects Disadvantages: 1- Recall Bias: relies on memory or past records the accuracy of, which may be uncertain difficult to validate the information obtained. 2- Selection of appropriate control group may be difficult. 3- We cannot measure incidence and can only estimate the relative risk. Family and Community Medicine| University of Benghazi | 2022-2023  50 B. COHORT STUDY Cohort: It is defined as a group of people who share a common characteristic or experience within a defined period (e.g. age, occupation, exposure to a drug, etc.). A cohort might be all those who survived a myocardial infarction in one particular year or people born on a particular date or year form as birth cohort. Features of cohort studies: 1. The cohort is identified prior to the appearance of the disease under investigation. 2. The study groups are observed(followed)over a period of time to determine the frequency of disease amongthem 3. The study proceeds forward from cause to effect. Indication for cohort studies: 1-When there is good evidence of an association between exposure and disease, as derived from clinical observations and supported by descriptive and case control studies. 2-When exposure is rare, but the incidence of disease is high among exposed e.g. special exposure groups like those in industries, exposure to X- rays. 3-When attrition of study population can be minimized, e.g. follow –up is easy, cohort is stable, co-operative and easily accessible. 4-When funds are available. The following general consideration are taken in to account: 1-Cohorts must be free from the disease under study. 2-As the knowledge of the disease permits, both the groups (i.e. study and control cohorts) should be equally susceptible to the disease under study, (e.g.; males over 35 years would be appropriate for studies on lung cancer. 3-The diagnostic and eligibility criteria of the disease must be defined beforehand. The groups are then followed, under the same identical conditions, over a period of time to determine the outcome of exposure onset of disease, disability or death., both the groups, in chronic disease such as cancer the time required for the follow –up may be very long. Family and Community Medicine| University of Benghazi | 2022-2023  51 Diagram illustrating cohort study design 1. Selection of study subjects: a. General population: when the exposure or cause of death is fairly distributed in the population, cohorts may be assembled from the general population, residing in a well- defined geographical area.eg. Framingham Heart study. If the population is very large, an appropriate sample is taken so that the result can be generalized to the population sampled. b. Special groups: i- Select groups: These may be professional groups e.g.: doctors, nurses, lawyer, teachers etc. These group are usually a homogeneous population, Doll’s prospective study on smoking and lung cancer was carried out on British doctors listed in medical register of the UK in 1951. These group are not homogeneous but they also offer advantages of accessibility and easy follow up for protracted period. ii. Exposure groups: Exposure to physical, chemical and other disease agents. A readily accessible source of these groups is workers in industries and those employed in high-risk situations (e.g. radiologists exposed to X-rays). 2. Obtaining data on exposure from Cohort members a-Cohort members, through personal interviews or mailed questionnaires offer a simple & economic way of obtaining information e.g. Doll &Hill. Family and Community Medicine| University of Benghazi | 2022-2023  52 b- Review of records: certain information (e.g. dose of radiation