Al-Quds University Faculty of Medicine, Introduction to Public Health Lecture 5, 2024-2025 PDF

Al-Quds University Faculty Of Medicine Introduction to Public Health (6106223) Lecture 5 2024-2025 1 Epidemiology : the foundation of Public Health 2 Introduction Epidemiology is t...

Al-Quds University Faculty Of Medicine Introduction to Public Health (6106223) Lecture 5 2024-2025 1 Epidemiology : the foundation of Public Health 2 Introduction Epidemiology is the basic science of public health, because it is the science that describes the relationship of health and/or disease with other health-related factors in human populations, such as human pathogens. Epidemiology has been used to generate much of the information required by public health professionals to develop, implement, and evaluate effective intervention programs for the prevention of disease and promotion of health such as the eradication of smallpox the anticipated eradication of polio and guinea worm disease and the prevention of heart disease and cancer. 3 Uses of epidemiology in support of public health 1. Describe the spectrum of the disease: disease represents the end point of a process of alteration of the host’s biological systems. 2. Describe the natural history of disease: epidemiological studies can be used to describe the natural history of disease to improve diagnostic accuracy. 3. Community diagnosis: epidemiological surveys are often used to establish the morbidity and mortality from specific diseases, to control the disease. 4. Describe the clinical picture of a disease: epidemiological strategies can identify who is likely to get a disease. 5. Identify factors that increase or decrease the risk of acquiring disease: having specific 4 characteristics increases the probability that What is epidemiology? The word itself comes from the Greek epi, demos, and logos; literally translated, it means the study (logos) of what is upon (epi) the people (demos). epi: “on or upon” + demos: “the (common) people” + logy: “study” =science of studying Determinants of diseases 5 What is Epidemiology ? The study of the frequency, distribution and determinants of states of health in human populations and the application of this study to control health problems and improve health outcomes. 6 7 Epidemiology The definition underscores that : 1. epidemiologists are concerned not only with disease but also with ‘health-related events’, and that ultimately epidemiology is committed to control of disease. 2. Epidemiology concerns itself with populations rather than individuals, thereby separating it from the rest of medicine and constituting the basic science of public health. 3. Following from this, therefore, is the need to describe health and disease in terms of frequencies and distributions in the population. 8 What is epidemiology? 1. Human disease does not occur at random. 2. Human disease has causal and preventive factors that can be identified through systematic investigation of different populations or subgroups of individuals within a population in different places or at different times. 3. Health is a state of equilibruim between agent, host(human ) and environment. 9  Epidemiology Key Terms Frequency : Prevalence, incidence Distribution: WHO (person)? WHERE (place)? WHEN(time)? Determinants: WHY?? causes of disease 10 Frequency Measurement of disease frequency : Amount of disease- risk, incidence rate and prevalence. These measurements give an idea about the burden of disease in a population. Incidence of disease is the number of new cases that develop within a given time period. Prevalence of a disease refers to the proportion of individuals in a population that has a disease at a particular time, sometimes also called the point prevalence. 11 12 Distribution By time Studying time trends for certain diseases. Three basic types of time trends are described: 1. Epidemic: a temporary increase in the incidence of a disease in a population. 2. Periodic: refers to the pattern of more or less regular changes in incidence (e.g whooping cough tends to peak every 3 years or so. 3. Secular or long –term trends, refer to non-periodic changes in disease statistics over a number of years (e.g. coronary heart disease). 13 Example of a Secular trend 14  In epidemiology, a secular trend refers to : the long-term pattern or trajectory of changes in the incidence, prevalence, or other health-related characteristics within a population over an extended period (typically years or decades). Secular trends help epidemiologists understand how health- related outcomes evolve, which can reflect broad shifts in society, the environment, public health practices, or medical interventions. These trends can be due to various factors, including Changes in population demographics (e.g., aging population)Environmental changes (e.g., pollution, climate change)Social or cultural shifts (e.g., changes in diet, and physical activity)Technological advances (e.g., improved diagnostics or treatments)Public health policies (e.g., vaccination campaigns, smoking bans) 15  These trends can be due to various factors, including: Changes in population demographics (e.g., aging population) Environmental changes (e.g., pollution, climate change) Social or cultural shifts (e.g., changes in diet, physical activity) Technological advances (e.g., improved diagnostics or treatments) Public health policies (e.g., vaccination campaigns, smoking 16 Distribution By Person Characteristics of person which affect the likelihood of occurrence of particular diseases include age, sex, ethnicity, occupation, socio- economic status, and marital status. Disease rates can be calculated for subsets of the population, therefore helping to identify priorities for preventive action. 17 18 Distribution By Place International, regional, and small area comparisons of disease distribution may be made. Standardization is required to allow for important differences in population structure! Examples Does the frequency of the disease vary from country to country? Does it vary among cities or neighborhoods? Does it vary within different parts of a large workplace? 19 20 21  Epidemiology Key Terms Endemic = disease that is present or usually prevalent in a population at all times in a particular geographical area. Malaria, for example, is considered endemic in certain countries and regions Outbreak = is used to describe a small, localized epidemic, often contained to a village or a small town. 22 Epidemiology Key Terms Epidemic = An unusually high occurrence of a disease or illness in a population or area. Pandemic = is an epidemic (an outbreak of an infectious disease) that spreads worldwide, or at least across a large region. 23 Epidemiology Key Terms Control: Reduced incidence or prevalence of a disease or condition; control measures are still required. Eradication: Permanent reduction to zero of the worldwide incidence of infection caused by a specific agent as a result of deliberate efforts; intervention measures are no longer needed. 24 Spectrum of disease risk 25 Epidemiology Key Terms Elimination of Infection: Reduction to zero of the incidence of infection caused by a specific agent in a defined geographic area as a result of deliberate efforts; continued measures to prevent reestablishment of transmission are required. 26 Epidemiology Key Terms Cluster: group of cases in a specific time and place that might be more than expected. Rate: number of cases occurring during a specific period; always dependent on the size of the population during that period (per /1000). 27  Example of a Disease Cluster: Legionnaires' Disease Outbreak in Flint, MichiganIn 2014-2015, Flint, Michigan, experienced a severe outbreak of Legionnaires' disease, a type of pneumonia caused by bacteria 28  Key factors that led to the cluster: Water source contamination: The city switched its water source to the Flint River, which was more corrosive than the previous source. This led to the leaching of lead from old pipes into the drinking water. Legionella bacteria: The water created conditions that favored the growth of Legionella bacteria, which can be found in warm, stagnant ‫ الراكدة‬water. 29  What are the objectives of epidemiology? 1. To determine the extent/frequency of disease (states of health) and/or behaviors in a community. 2. To identify the etiology or the cause/s of a disease and the factors that impact upon a person’s risk for a disease. 3. To study the natural history and prognosis of disease. 30  What are the objectives of epidemiology? 4. To evaluate new preventive and therapeutic measures and new modes of health care delivery. 5. To provide the foundation for developing public policy and regulatory decisions relating to public health problems. 31 Differences between basic, clinical and public health science 32 Differences between basic, clinical and public health science 33  In the lab… Mostly experimental Variables controlled by the investigator Highly equipment intensive All (or most) variables known Valid results (usually) Replication relatively easy Results are sometimes uncertain for humans Little need for statistical manipulation of data 34  In the community… Mostly observational Variables controlled by “nature” Highly labor intensive Some variables are unknown Validity of data often questionable Replication difficult/impossible  The meaning of results for humans is clear Statistical control is often very important 35  Epidemiology is often interested in biological phenomenon with normal distributions (e.g., blood pressure, birth weight, adult weight, IQ Normal distributions (e.g., blood pressure, birth weight, adult weight, IQ). 36 Disease states are often linked to the tails of some normally distributed phenomenon Because epidemiology is usually interested in cases of illness/disease, it is generally more interested in the tails of the distribution than in the entire distribution. 37 A physiologist may study blood pressure, the epidemiologist will probably study hypertension. The nutritionist studies adult weight, the epidemiologist studies obesity. 38  “A major challenge for epidemiology today is to become an effective instrument in the shaping and evaluation of health policies and practices… Epidemiologists must obtain and analyze the information needed and present it to health planners in such a way that this information can be used in policy, planning, and evaluation. Michel Thuriaux, Epidemiology and Statistics Unit, WHO Regional Office for Europe, 1992 39  However, as epidemiologists/public health practitioners, we most often need to act/intervene under conditions of uncertainty based on the available evidence 40  Types of Epidemiology  Descriptive Epidemiology  Analytical Epidemiology 41 Why Conduct Studies? To describe burden of disease or prevalence of risk factors, health behaviors, or other characteristics of a population that influence risk of disease To determine causes or risk factors for illness To determine relative effectiveness of interventions 42  Descriptive or Analytic Studies? 1. Descriptive Epidemiology:  Examines the distribution of a disease/behavior/state of health in a defined population, and observes the features of its distribution in terms of person, place and time.  Descriptive studies ; Generate hypotheses Answer What? Who? Where? When? 43 Descriptive Epidemiology Description of disease occurrence, by person, place and time. Not intended to confirm causes. 44  2. Analytical Epidemiology Hypothesis-testing Tests a specific hypothesis about the relationship between a disease/behavior/ state of health and a putative ‫ مفترض‬cause, by conducting epidemiologic investigations that relates the exposure of interest to the outcome of interest (or not) Answers how? and Why ? 45  Determinants of variations in morbidity and mortality Proximate determinants: Factors that directly influence the risk of disease and the outcomes of disease processes in individuals. Distal (underlying) determinants: Social, economic and cultural factors that influence the health status of a population and its members through one or more of the proximate causes. 46  Proximate determinants of morbidity and mortality Personal behaviors: diet, hygiene, physical activity, alcohol and tobacco use, sexual behavior, etc. Environmental exposures: exposure to infectious, chemical or physical agents, occupational hazards, etc. Nutrition: Under-nutrition, micronutrient deficiency, obesity. Injuries: intentional or accidental injuries Personal illness control: specific preventive and sickness care actions. 47  Distal determinants of morbidity and mortality Socio-economic factors: personal and household wealth, community development, women education & employment. Institutional factors: health systems, health regulations/laws, technological development, environmental interventions. Cultural factors: traditional beliefs about illness & health, religious values, role & status of women, etc. Broader context: political economy, transportation and communication systems, etc. 48 49  Analytical Epidemiology Researcher attempts to control external influences by careful selection of subjects and/or statistical adjustments. Analytic studies test hypotheses about exposure outcome relationships Measure the association between exposure and Outcome. Include a comparison group Observational or Experimental study designs. 50  HOST The Analytical Epidemiological NT Triad E M AG O N R E I NT NV E 51 1. AGENTS Nutrients Poisons Allergens Radiation Physical trauma Microbes Psychological experiences 52 2. HOST FACTORS Age Genetic endowment Immunologic state Personal behavior 53 3. ENVIRONMENT Crowding Atmosphere Modes of communication (phenomena in the environment that bring host and agent together, such as vector, vehicle, reservoir). 54 5 Rubrics ‫ قواعد‬of Epidemiology Anthony JC et al., 2005 HOW WHERE? MAN Y? WHAT WHY? HOW? NOW? 55 5 Rubrics of Epidemiology HOW MAN Y? Quantity: How many people in the population are affected as cases (prevalence), or are becoming cases (incidence)? 56  5 Rubrics of Epidemiology WHERE? Location: Where in the population are affected cases more likely to be found with respect to characteristics, conditions, and processes of person, place & time? 57 5 Rubrics of Epidemiology WHY? Causes: What accounts for some people becoming affected and not others? 58  5 Rubrics of Epidemiology HOW? Mechanisms: What sequences of states and processes influence who becomes and remains a case and who does not? 59  5 Rubrics of Epidemiology WHAT NOW? Prevention & Intervention: What can be done to prevent or delay onset of suffering, shorten its duration, and reduce the burden of disease from affected cases, their families, and society in general? 60  Health States of PH Importance Death – not whether, but why and when (age). Disease – a cluster of signs, symptoms and laboratory findings linked by a common patho- physiologic sequence, and that can cause human distress. Illness – subjective state of the individual who feels aware of not being well. – The ill person may or may not be suffering from disease. Sickness – the social role assumed by an individual suffering from an illness. 61  Health States of PH Importance Disability & Handicap – difficulty in performing expected functions, especially those important to ordinary human life, i.e. interfering with work, activities of daily living, etc. Destitution – ‫العوز‬the economic burden imposed by a health state Dysfunction, Discomfort, Dissatisfaction. 62 63 Natural history of disease in the community a) Distribution of health and disease Persons Persons with C exposed disease Outcome o or at risk manifestation m + + m Death u Disability n - - Recovery Factors i determining Factors T disease determining Factors determining y initiation / disease outcome. risk manifestation b) Factors determining distribution 64 Summary Epidemiology is the core science of public health because it defines health and disease in human populations, describes disease etiology, and evaluates public health control efforts. It achieves these goals through a variety of strategies and methods. Epidemiology is a dynamic science that is continually evolving new strategies and methods in support of public health goals. 65 “Epidemiology functions as a lens through which a clinician can see along the dimension that stretches beyond the individual patient and beyond the threshold of the clinic/hospital, toward the population from which the patient came” - Anthony et al., 1997 66 67