Introduction to Epidemiology Lecture Notes 2024 PDF

Introduction to Epidemiology  Learning outcomes: By the end of this module participants should be able to understand: Epidemiology definitions Core functions & key concepts Different Morbidity Rates Design study Determinants of disease Types of Risk Factors Some examples of ris...

Introduction to Epidemiology  Learning outcomes: By the end of this module participants should be able to understand: Epidemiology definitions Core functions & key concepts Different Morbidity Rates Design study Determinants of disease Types of Risk Factors Some examples of risk factors in epidemiology  Epidemiology definitions Epidemiology is study of the distribution and determinants (factors) of health-related states or events in specified populations, and the application of this study to the control of health problems. Epidemiology is a fundamental science of public health that focuses on understanding the distribution, determinants, and control of health and disease in populations. It is a discipline that combines elements of biology, social sciences, statistics, and medicine to study patterns of health and illness. Epidemiology definitions: Other Definitions:  Beyond the basic definition, epidemiology is also understood as: The method used to find the causes of health outcomes and diseases in populations. This science of public health uses systematic and data- driven approaches to understand the pattern of health- related states or events.  Core Functions of Epidemiology Epidemiology serves to identify the frequency, patterns, and causes of diseases in populations. It helps in planning and evaluating strategies to prevent illness and as a guide to managing patients in whom the disease has already developed. Key Concepts: ⚬Distribution: Investigates who is affected by a disease, when, and where. ⚬Determinants: Studies the factors that influence disease occurrence, including biological, environmental, and lifestyle factors. ⚬Control of Health Problems: Applies research findings to develop interventions to prevent and control health issues.  Methodology: Epidemiologists use various study designs to Epidemiology is vital investigate health-related events (such as for the continuous cross-sectional, cohort, and case-control improvement of public health, studies). They also employ statistical analysis providing the to interpret data and make informed evidence base for health policy and conclusions about health risks. actions. Public Health Impact: The insights gained from epidemiological studies shape public health policies and practices by identifying risk factors for  Comparative role of Public Health Professional and Epidemiologist Public Health Professional Role: A public health professional develops and implements programs to promote population/community health and well-being. Example: Designing and leading a national campaign to reduce tobacco use through policy advocacy, awareness creation, and community-based interventions. Epidemiologist Role: An epidemiologist studies disease patterns, causes, and effects to inform public health decisions. Example: Investigating a cholera outbreak in a region to identify the source, mode of transmission, and risk factors, and recommending control measures to prevent  Roles During the COVID-19 Outbreak Public Health Professional Role: Leading the overall response to the pandemic by coordinating strategies at local, national, and global levels. Example: o Developing public awareness campaigns to promote mask-wearing, hand hygiene, and vaccination. o Advising governments on policies such as lockdowns and travel restrictions. o Establishing infrastructure for mass vaccination programs and testing sites.  Roles During the COVID-19 Outbreak Epidemiologist Role: Investigating the spread, patterns, and determinants of COVID-19 to provide evidence for control measures. Example: o Analyzing data on infection rates (total cases, new cases), hospitalizations and deaths to identify hotspots and predict future trends. o Conducting contact tracing to break transmission chains. o Studying vaccine effectiveness and the impact of its variants to guide immunization strategies. Both Public Health Professional and Epidemiologist played a critical role in mitigating the  Distribution of Disease ⚬Person (who): Looks at the characteristics of individuals that affect their likelihood of becoming ill, such as age, sex, ethnicity, occupation, and behaviors. ⚬Time (when): Refers to the temporal (time related) distribution of diseases, including trends over time and seasonal variations. ⚬Place (where): Involves the study of geographical  Morbidity Morbidity has been defined as any deviation, subjective or objective, from a state of physiological or psychological well- being. Measures of morbidity frequency characterize the number of persons in a population who newly become ill (incidence) or were already ill at a given time (prevalence).  Rate In epidemiology, a rate is a measure of the frequency with which an event occurs in a defined population over a specified period of time.  Morbidity Rates Incidence Rate: Is the number of new cases (of disease or event) in a specified population during a specified period of time, usually expressed per 100,000 individuals (e.g. new cases of measles among children). It is calculated as: Incidence Rate= No. of new cases × 100,000 Population at Risk Morbidity Rates: Attack Rate: Is a specific incidence rate for a particular disease over a specific period of time. It measures the risk of disease among those people exposed to a certain exposure (e.g. food poisoning because of eating contaminated mashed potatoes). Morbidity Rates: Prevalence Rate: Is the total number of individuals who already have an attribute or disease at a particular time, divided by the population at risk of having the attribute or disease at that time (e.g. prevalence of hypertension in a community). It is calculated as: Prevalence Rate= Total number of cases with attribute or disease × 100,000 Total Population at risk Morbidity Rates: Relationship between Incidence and Prevalence In a steady-state situation, in which the rates are not changing and population is stable, the following equation applies: Prevalence = Incidence × Duration of Disease Study Designs: Study designs Are a crucial element in epidemiology for investigating the distribution, patterns, and determinants of diseases. Common study designs used in Epidemiology: Observational Studies: These do NOT involve any manipulation by the researcher. Instead, the researcher observes & records information as it occurs naturally. Case Reports and Case Series: Are detailed presentations of a single patient or a group of patients with a similar diagnosis. Common study designs used in Epidemiology, cont: Cross-sectional Studies: Assess the prevalence of health outcomes or determinants of health in a population at a single point in time. Eg.: Prevalence for cases of lung cancer among smokers at a point of time. Case-control studies: Compare individuals with a disease (cases) to those without the disease (controls) to identify the risk factors that may contribute to occurrence of the disease retrospectively. Eg. Comparing lung cancer smokers with normal smokers. Cohort Studies: Follow a group of people over time to see how their exposures affects their outcomes. Eg. Following smokers over time to look for developing lung cancer. Cross-sectional Design factor present No Disease factor absent Study population factor present Disease factor absent time Study only exists at this point in time  factor present Case-Control Design Cases (disease) factor absent Study population factor present Controls (no disease) factor absent present past time Study begins here  Cohort study Exposed Outcome Measure exposure Baseline Non-exposed Outcome time Study begins here Common study designs used in Epidemiology, cont…: Experimental Studies: These involve some level of intervention by the researcher, such as the administration of a treatment or a behavior change. ⚬Randomized Controlled Trials (RCTs): Participants are randomly assigned to either the intervention group or the control group to measure the effect of the intervention. ⚬Community Trials: Are similar to RCTs, but the units of randomization are communities or groups rather than individuals.  RANDOMIZATION outcome Experimental Design Intervention no outcome Study population outcome Control no outcome baseline future time Study begins here (baseline point) Common study designs used in Epidemiology, cont…: Ecological Studies: Examine the relationship between exposure and disease with data at the group level rather than the individual level. Meta-Analyses: Combine data from multiple studies to derive conclusions that have greater statistical power due to the increased sample size.  Importance of Study Designs Each study design has its strengths and weaknesses and is chosen based on the research question, ethical considerations, and practical constraints. For instance, RCTs are considered the gold standard for determining causality but may not always be feasible or ethical. Observational studies are more common when RCTs are not possible, but they may be more prone to bias. Understanding these study designs is essential for interpreting the results of epidemiological research and for designing studies that can provide reliable and valid data for public health decision-making.  Determinants of Disease Determinants of disease are the factors that can influence the occurrence of disease and include a wide range of forces, from genetic to environmental factors. Determinants of disease can be classified into: ⚬Biological: Genetics, age, sex. ⚬Environmental: Living conditions, climate, pollution. ⚬Behavioral: Lifestyle choices, dietary habits. ⚬Social: Socioeconomic status, community support networks.  Risk Factors In epidemiology, risk factors are characteristics or conditions that increase the likelihood of a person developing a disease or health problem. They can be environmental, biological, behavioral, or social.  Some examples of risk factors in epidemiology Biological Factors: Such as age, sex, genetics, and ethnicity. Environmental Factors: Including exposure to pollutants, climate, and living conditions. Behavioral Factors: Like smoking, alcohol consumption, diet, and physical activity. Socioeconomic Factors: Such as education level, income, and occupational hazards. It is important to note that having one or more risk factors does not mean that a person will definitely develop a disease, but it does increase the chances compared to individuals without the risk factors.  Determinants of Disease Types of Risk Factors: o Modifiable: These are factors that can be changed, such as lifestyle habits, including smoking, diet, and exercise. o Non-modifiable: These include factors that cannot be changed, like age, gender, and genetic predisposition.  Determinants of Disease Measuring Risk: Epidemiologists often use measures such as incidence rates and prevalence proportions to quantify the risk associated with certain factors. Causality: It refers to the Causative Factors for any disease. Risk factors can be associated with a higher likelihood of disease, they do not necessarily cause the disease. Establishing causality requires further research and evidence.  Determinants of Disease Interactions: Multiple risk factors can interact in complex ways to influence the likelihood of developing a disease. For example, the risk of heart disease is influenced by many factors, such as: diet, exercise, smoking, and genetic factors (multifactorial causes). Understanding risk factors is crucial for developing prevention strategies and health policies aimed at reducing the incidence of diseases and improving public health outcomes. Challenges in the field of Epidemiology Challenges or limitations within the field of Epidemiology that could affect the accuracy or validity of epidemiological studies may include: 1. Data Quality: Inaccurate or incomplete data can lead to erroneous conclusions. 2. Bias: Systematic errors in the design or conduct of a study can distort results. 3. Confounding Variables: Factors that are related to both the exposure and the outcome can mislead the association between them. 4. 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