Epidemiology - A Brief Introduction PDF

Epidemiology A Brief Introduction Epidemiology - definition  epi – means “on, upon, befall”.  epidermis: upon the body, skin.  Demo = demos – means “people, population, man”.  demographics  Ology = logos – means study of  Literally epidemiology: that which...

Epidemiology A Brief Introduction Epidemiology - definition  epi – means “on, upon, befall”.  epidermis: upon the body, skin.  Demo = demos – means “people, population, man”.  demographics  Ology = logos – means study of  Literally epidemiology: that which befalls man Epidemiology - definition  Some see epidemiology as science, others see it as a method.  Generally seen as a scientific method to investigate disease.  Def: an investigative method used to detect the cause or source of diseases, disorders, syndromes, conditions, or perils that cause pain, injury illness, disability, or death in human populations or groups. Epidemiology – What is it?  The study of the nature, cause, control, and determinants of the frequency and distribution of disease, disability, and death in human populations in terms of the causal factors.  Also involves characterizing the distribution of heath status, diseases, or other health problems in terms of age, sex, race, geography, religion, education, occupation, behaviors, time, place, person, etc. Epidemiology – What is it?  Serves as the foundation and logic of interventions made in the interest of public health and preventive medicine.  It is considered a cornerstone methodology of public health research, and is highly regarded in evidence-based medicine for identifying risk factors for disease and determining optimal treatment approaches to clinical practice. Epidemiology – What is it?  In the work of communicable and non- communicable diseases, the work of epidemiologists range from outbreak investigation to study design, data collection and analysis including the development of statistical models to test hypotheses and the documentation of results for submission to peer-reviewed journals.  Epidemiologists may draw on a number of other scientific disciplines such as biology in understanding disease processes and social science disciplines including sociology and philosophy in order to better understand proximate and distal risk factors. Epidemiology – What is it?  Study of the distribution and determinants of health-related states or events among specified populations and the application of that study to the control of health problems. Epidemiology – What is it? Key terms in this definition reflect some important principles of epidemiology, these key terms include: 1. Study. 2. Distribution. 3. Determinants. 4. Health-related states or events. 5. Specified populations. 6. Application. Key Terms of Epidemiology Definition: 1. Study: Epidemiology is a scientific discipline. Epidemiology is data-driven and relies on systematic and unbiased approach to collection, analysis, and interpretation of data. Epidemiology draws on methods from other scientific fields, e.g. biostatistics and informatics, with biologic, economic, social, and behavioral sciences. Key Terms of Epidemiology Definition cont.: 1. Study cont.: Epidemiology is described as the basic science of public health, not just a research activity but an integral component of public health. Why? a. Epidemiology is a quantitative discipline that relies on knowledge of probability, statistics and research methods. b. Epidemiology is a method of causal reasoning based on developing and testing hypotheses. Key Terms of Epidemiology Definition cont.: 2. Distribution: Epidemiology is concerned with frequency and pattern of health events in a population: Frequency refers not only to number of health events such as number of cases of diabetes in a population, but also to relationship of that number to size of population. The resulting rate allows epidemiologists to compare disease occurrence across different populations. Key Terms of Epidemiology Definition cont.: 2. Distribution cont.: Pattern refers to occurrence of health-related events by time, place, and person. Time patterns may be annual, seasonal, daily, etc. Place patterns include geographic variation, urban/rural differences, and location. Personal characteristics or demographic factors e.g. age, sex, marital status, and environmental exposures. Characterizing health events by time, place, and person are activities of descriptive epidemiology. Key Terms of Epidemiology Definition cont.: 3. Determinants: Epidemiology is also used to search for determinants, which are causes and other factors that influence the occurrence of disease and other health-related events. To search for these determinants, epidemiologists use analytic epidemiology to provide the “Why” and “How” of such events. Key Terms of Epidemiology Definition cont.: 4. Health-related states or events: Epidemiology focused on chronic diseases, injuries, birth defects, occupational and environmental health. Epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise. Now, with recent molecular methods, epidemiologists can examine genetic markers of disease risk. Term health related states or events may be anything that affects the well-being of a population. Nonetheless, many epidemiologists still use term “disease” for wide range of health-related states and events. Key Terms of Epidemiology Definition cont.: 5. Specified populations Epidemiologists and direct health-care clinicians are both concerned with occurrence and control of disease, they differ greatly that clinician is concerned about individual; epidemiologist concerned about people in a community or population. For example, when a patient with diarrheal disease, both are interested in correct diagnosis. However, clinician focuses on treating individual, epidemiologist focuses on identifying source of illness; number of cases and interventions to prevent additional cases or recurrences. Key Terms of Epidemiology Definition cont.: 6. Application: Epidemiology is not just “study of” health in a population; it also involves applying the knowledge gained by the studies to community-based practice. Epidemiologist uses scientific methods of descriptive and analytic epidemiology as well as experience, epidemiologic judgment in “diagnosing” the health of a community and proposing appropriate, practical, and acceptable public health interventions to control and prevent disease in the community. Key Terms of Epidemiology Definition cont.: Summary Epidemiology is study (scientific, systematic, data- driven) of the distribution (frequency, pattern) and determinants (causes, risk factors) of health-related states and events (not just diseases) in specified populations (patient is community, individuals viewed collectively), and the application of (since epidemiology is a discipline within public health) this study to control of health problems. Purposes of Epidemiology  To explain the etiology (cause) of a single disease or group of diseases using information management.  To determine if data are consistent with proposed hypothesis.  To provide a basis for developing control measures and prevention procedures for groups and at risk populations. Purposes of Epidemiology 1. Discover the agent, host, and environmental factors that affect health. 2. Determine the relative importance of causes of illness, disability, and death. 3. Identify those segments of the population that have the greatest risk from specific causes of ill health. 4. Evaluate the effectiveness of health programs and services in improving population health. Terms to know  Disease a pattern of response by a living organism to some form of invasion by a foreign substance or injury which causes an alteration of the organisms normal functioning.  also – an abnormal state in which the body is not capable of responding to or carrying on its normally required functions.  Pathogens organisms or substances such as bacteria, viruses, or parasites that are capable of producing diseases.  Pathogenesis the development, production, or process of generating a disease.  Pathogenic means disease causing or producing.  Pathogenicity describes the potential ability and strength of a pathogenic substance to cause disease. Terms to know  Infective diseases are those which the pathogen or agent has the capability to enter, survive, and multiply in the host.  Virulence the extent of pathogenicity or strength of different organisms.  the capacity and strength of the disease to produce severe and fatal cases of illness.  Invasiveness the ability to get into a susceptible host and cause a disease within the host.  The capacity of a microorganism o enter into and grow in or upon tissues of a host.  Cluster group of cases in a specific time and place that might be more than expected. Terms to know  Etiology the factors contributing to the source of or causation of a disease.  Toxins a poisonous substance that is a specific product of the metabolic activities of a living organism and is usually very unstable.  notably toxic when introduced into the tissues, and typically capable of inducing antibody formation.  Antibiotics a substance produced by microorganism or a semisynthetic substance derived from a microorganism and able in dilute solution to inhibit or kill another microorganism. Terms to know  Incidence the rate of new cases of a disease occurring in a specific population over a particular period of time.  Two types of incidence are commonly used: ‘incidence proportion’ and ‘incidence rate’.  Incidence proportion, risk or cumulative incidence refers to the number of new cases in your population during a specified time period. It can be calculated using the following equation: Terms to know  Incidence rate incorporates time directly into the denominator and can be calculated as follows:  Person years at risk means the total amount of time (in years) that each person of the study population is at risk of the disease during the period of interest. Terms to know  Prevalence the number of cases of a disease in a specific population at a particular time point or over a specified period of time.  Prevalence can either refer to ‘point prevalence’ or ‘period prevalence’.  Point prevalence is the proportion of people with a particular disease at a particular time point and can be calculated as follows: Terms to know  Period prevalence is the proportion of people with a particular disease during a given time period.  Prevalence is a useful measure of the burden of disease.  Prevalence changes relate with condition are cured or die. Increased prevalence doesn’t necessarily mean a bigger problem. Higher prevalence could mean a prolonged survival without cure or an increase of new cases, or both. A lower prevalence could mean that more people are dying rather than being cured, a rapid recovery, and/or a low number of new cases. Terms to know  Prevalence differs from incidence proportion as prevalence includes all cases (new and pre-existing cases) in the population at the specified time whereas incidence is limited to new cases only.  The factor connecting prevalence and incidence statistics is the length of time the disease is present for before patients die, or are cured.  Prevalence relies on 2 factors:  How many people have had the disease in the past.  Duration of the disease in the population. Prevalence vs incidence The Epidemiology Triangle  Outbreaks in a population often involves several factor and entities.  Many people, objects, avenues of transmission, and organisms can be involved in the spread of disease  Epidemiologist have created a model to help explain the multifaceted phenomena of disease transmission: the epidemiology triangle. Time The Epidemiology Triangle  Many diseases rely on an agent or single factor for an infectious disease to occur.  Epidemiologist use an ecological view to assess the interaction of various elements and factors in the environment and disease-related implications.  When more than a single cause must be present for a disease to occur, this is called multiple causation. The Epidemiology Triangle The interrelatedness of 4 factors contribute to the outbreak of a disease: 1. Role of the host. 2. Agent. 3. Environmental circumstances. 4. Time. The epidemiology triangle is used to analyze the role and interrelatedness of each of the four factors in epidemiology of infectious diseases, that is the influence, reactivity and effect each factor has on the other three. The Epidemiology Triangle  The agent is the cause of the disease  Can be bacteria, virus, parasite, fungus, mold  Chemicals (solvents), Radiation, heat, natural toxins (snake or spider venom)  The host is an organism, usually human or animal, that harbors the disease  Pathogen disease-causing microorganism or related substance  Offers subsistence and lodging for a pathogen  Level of immunity, genetic make-up, state of health, and overall fitness within the host can determine the effect of a disease organism can have upon it. The Epidemiology Triangle  The environment is the favorable surroundings and conditions external to the human or animal that cause or allow the disease or allow disease transmission  Environmental factors can include the biological aspects as well as the social, cultural, and physical aspects of the environment  Time accounts for incubation periods, life expectancy of the host or pathogen, duration of the course of illness or condition. The Epidemiology Triangle  The mission of the epidemiologist is to break one of the legs of the triangle, which disrupts the connection between environment, host, and agent, stopping the continuation of an outbreak.  The goals of public health are the control and prevention of disease.  By breaking one of the legs of the triangle, public health intervention can partially realize these goals and stop epidemics.  An epidemic can be stopped when one of the elements of the triangle is interfered with, altered, changed or removed from existence.  1. Agent Agent is the first link in the chain of disease transmission. In the development of disease, agent is the foremost factor. It can be living or non-living. The disease agent include 6 broad groups: a. Biological agent. b. Nutritional agent. c. Chemical agent. d. Mechanical agent. e. Physical agent. f. Social agent. a. Biological agents  They are living agents found in man, animals, insects, soil and air.  These agents are poisonous, spread infections and generate disease.  They include virus, bacteria, protozoa and fungi. b. Nutritional agents  Nutrients are essential for keeping individual healthy. An excess or deficiency of intake of these nutrients can lead to nutritional deficiency disorders.  Nutritional agents include proteins, fats, carbohydrate, vitamins, minerals and water.  Disorders due to nutrients: PEM (Protein energy malnutrition), Anemia, Goiter, Obesity and Vitamins deficiencies. b. Nutritional agents cont. Vitamin/Mineral Deficiency disease/ Symptoms disorder Vitamin A Loss of vision Poor vision, loss of vision in darkness (night), sometimes complete loss of vision. Vitamin B1 beriberi Weak muscles and very little energy to work. Vitamin C Scurvy bleeding gums, wounds take longer time to heal Vitamin D rickets Bones become soft and bent. b. Nutritional agents cont. Vitamin/Mineral Deficiency disease/ Symptoms disorder Bone and tooth Weak bones, tooth Calcium decay decay. Glands in the neck swollen, mental Iodine Goiter disability in children. Iron Anemia Weakness. c. Chemical agents  Chemical agents which affect human are two types: Endogenous and exogenous. i. Endogenous chemical agents which are produced and present in human body. Excess or less result in illness. e.g. Serum bilirubin (excess lead to jaundice). Urea (Ureamia). Ketones (ketosis). Uric acid (Gout). Calcium carbonate (kidney stones). c. Chemical agents cont. ii. Exogenous chemical agents which are present outside the human body. e.g.  Gases, metals, dust, smoke, fumes.  Insecticides and allergens. These agents may be acquired by inhalation, ingestion or inoculation. d. Mechanical agents  Exposure to chronic friction and other mechanical forces may result in crushing, tearing, dislocation, injuries, fractures and even death. e. Physical agents  Exposure to excessive heat, cold, humidity, pressure, radiation, electricity and sound may cause the various disease. f. Social agents  Social agents like poverty, illiteracy, population explosion, unhealthy life style, drinking, drugs and other addictions, social isolation are also responsible for many diseases.  2. Host Factors  Host factor is the human body where the disease agent stay, grow and multiply to produce illness.  In epidemiology terminology, the human host is referred to as soil and the disease agent as seed.  Host factors may classified as: i. Demographic characteristics. ii. Biological characteristics. iii. Social and economic characteristics. iv. Life style factors. i. Demographic factors  These include age and sex. Some disease are common in childhood (e.g. Measles, PEM) and some disease are more prevalent in old age (enlargement of prostate gland, cataract and osteoporosis).  Similarly there are certain diseases which affect women more and other are in men only. ii. Biological factors  Some diseases are common in some specific individual only. E.g. diseases depend on the structure of genes or genetic diseases, blood diseases, diabetes and hypertension. iii. Socioeconomic factors  Onset of the disease is also affected by the economic and social status of the individuals such as education, habits and marital condition. iv. Life style  Moral values, habits, nutrition, physical labour, consumption of alcohol, drug addiction, smoking etc. also affect onset of the diseases. E.g. people those who are addicted to drugs or alcohol, are more likely to fall ill. 3.  3- Environmental Factors  It has been proved that polluted environment is responsible for many diseases.  Environmental factors are classified into 3 groups: i. Physical environment. ii. Biological environment. iii. Physiological environment. i. Physical environment  Air, house, season, water, temperature, light, noise, radiation, disposal of sewage, etc., are the physical factors which affects the environment. ii. Biological environment  These include organisms (animals, insects, rodents) which can cause diseases. iii. Physiological environment  Standards of living e.g. culture, education are related to the onset of disease directly or indirectly. Disease Transmission  Fomites: inanimate objects that serve as a role in disease transmission, e.g. Pencils, pens, doorknobs, infected blankets.  Vector: any living non-human carrier of disease that transports and serves the process of disease transmission, E.g. Insects: fly, flea, mosquito; rodents; deer.  Reservoirs: humans, animals, plants, soils or inanimate organic matter (feces or food) in which infectious organisms live and multiply. Humans often serve as reservoir and host.  Zoonosis: when a animal transmits a disease to a human. Disease Transmission  Carrier: one that spreads or harbors an infectious organism.  Some carriers may be infected and not be sick. e.g. Typhoid Mary  Mary Mallon (1869 – 1938) was the first person in the United States to be identified as a healthy carrier of typhoid fever. Over the course of her career as a cook, she infected 47 people, three of whom died from the disease.  Her notoriety is in part due to her vehement denial of her own role in spreading the disease, together with her refusal to cease working as a cook.  She was forcibly quarantined twice by public health authorities and died in quarantine. It is possible that she was born with the disease, as her mother had typhoid fever during her pregnancy. Disease Transmission  Active carrier: individual exposed to and harbors a disease-causing organism. May have recovered from the disease.  Convalescent carrier: exposed to and harbors disease-causing organism (pathogen) and is in the recovery phase but is still infectious.  Healthy carrier: exposed to an harbors pathogen, has not shown any symptoms. Disease Transmission  Incubatory carrier: exposed to and harbors a disease and is in the beginning stages of the disease, showing symptoms, and has the ability to transmit the disease.  Intermittent carrier: exposed to and harbors disease and can intermittently spread the disease.  Passive carrier = Healthy carrier: exposed to and harbors disease causing organism, but has no signs or symptoms. Modes Disease Transmission  Modes of disease transmission  methods by which an agent can be passed from one host to the next.  or can exit the host to infect another susceptible host (either person or animal).  Two general modes  Direct.  Indirect. Modes Disease Transmission  Direct transmission or person to person  Immediate transfer of the pathogen or agent from a host/reservoir to a susceptible host.  Can occur through direct physical contact or direct personal contact such as touching contaminated hands.  Indirect transmission  Pathogens or agents are transferred or carried by some intermediate item or organism, means or process to a susceptible host  one or more following ways: airborne, waterborne, vehicleborne, vectorborne. Modes Disease Transmission  Indirect transmission  Airborne:  Droplets or dust particles carry the pathogen to the host and infect it.  Sneezing, coughing, talking all spray microscopic droplets in the air.  Waterborne:  Carried in drinking water, swimming pool, streams or lakes used for swimming. Examples: cholera.  Vehicleborne:  Related to fomites.  Vectorborne:  A pathogen uses a host (fly, flea, louse, or rat) as a mechanism for a ride or nourishment this is mechanical transmission, biological transmission when the pathogen undergoes changes as part of its life cycle, while within the host/vector and before being transmitted to the new host. Chain of Transmission  Close association between the triangle of epidemiology and the chain of transmission.  Disease transmission occurs when the pathogen or agent leaves the reservoir through a portal or exit and is spread by one of several modes of transmission.  Breaks in the chain of transmission will stop the spread of disease. Etiological Mode of agent/pathway transmission Source / Host Reservoir Classes of Epidemics / Outbreaks  Common Source Epidemic – when a group of persons is exposed to a common infection or source of germs.  Point source from a single source (food).  Persons exposed in one place at one time and become ill within the incubation period.  Ex: bad mayonnaise at a picnic.  Intermittent irregular and somewhat unpredictable.  Tuberculosis spread by person to person contact and people move around and interact with other people.  Continuous epidemic  When an epidemic spreads through a community or population at a high level, affecting a large number of people within the population without diminishing. Classes of Epidemics / Outbreaks  Propagated Epidemic when a single source cannot be identified, yet the epidemic or diseases continues to spread from person to person.  Usually experiences exponential growth.  Cases occur over and over longer than one incubation period.  Mixed Epidemic a common source epidemic is followed by person-to-person contact and the disease is spread as a propagated outbreak. Levels of Disease Diseases have a range of seriousness, effect, duration, severity, and extent. Classified into 3 levels:  Acute relatively severe, of short duration and often treatable. usually the patient either recovers or dies.  Subacute intermediate in severity and duration, having some acute aspects to the disease but of longer duration and with a degree of severity that detracts from a complete state of health  Patient expected to eventually heal.  Chronic less severe but of long and continuous duration, lasting over a long time periods, if not a lifetime.  Patient may not fully recover and the disease can get worse overtime.  Life not immediately threatened, but may be over long term. Immunity and Immunization  History  Before polio vaccine became available in 1955, 58,000 cases of polio occurred in peak years. ½ of these cases resulted in permanent paralysis.  Prior to measles vaccine in 1963, 4,000,000 cases per year.  Immunization of 60 million children from 1963- 1972 cost $180 million, but saved $1.3 billion.  Mumps used to be the leading cause of child deafness.  10% of children with diphtheria died. Immunity and Immunization  Types of immunity possible in humans: 1. Innate (Natural) immunity occurs before microbe exposure e.g. skin & mucous membranes. 2. Adaptive (Acquired) Immunity obtained by having had a dose of a disease that stimulates the natural immune system or artificially stimulating immune system. a. Active Immunity body produces its own antibodies after contact with foreign antigens. b. Passive Immunity through the introduction of already preformed antibodies. Immunity  When there is little to no immunity within a population, the disease spreads quickly. Immunity Herd Immunity  the resistance a population or group (herd) has to the invasion and spread of an infectious disease. Diseases for which vaccines are used  Antrhax  Pneumonia  Chicken pox  Polio  Cholera  Rabies  Diphtheria  Small pox  German measles (rubella)  Spotted fever  Hepatitis A & B  Tetanus  Influenza  Tuberculosis  Malaria (in process)  Typhoid Fever  Measles  Typhus  Menigitis  Whooping Cough  Mumps  Yellow Fever  Plague