Introduction to Epidemiology

Introduction to Epidemiology

• Epidemiology is the study of the distribution and determinants of health-related states or events in specific populations, and the application of this study to the control of health problems.
• It's a fundamental science of public health that focuses on understanding the distribution, determinants, and control of health and disease in populations.
• Epidemiology combines elements of biology, social sciences, statistics, and medicine to study patterns of health and illness.

Learning Objectives

• Participants should understand epidemiology definitions.
• Participants should understand core functions and key concepts in epidemiology.
• Participants should understand different morbidity rates.
• Participants should understand study design methods in epidemiology.
• Participants should understand determinants of disease.
• Participants should understand types of risk factors.
• Participants should understand examples of risk factors in epidemiology.

Epidemiology Definitions

• Epidemiology is the study of the distribution and determinants (factors) of health-related states or events in specific 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's a discipline that combines elements of biology, social sciences, statistics, and medicine to study patterns of health and illness.
• Epidemiology is a method of finding causes of health outcomes and diseases in populations.
• It utilizes systematic and data-driven approaches to understand patterns of health-related states or events.

Core Functions of Epidemiology

• Epidemiology identifies the frequency, patterns, and causes of diseases in populations.
• It helps in planning and evaluating strategies to prevent illness and 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 utilize various study designs to investigate health-related events, such as cross-sectional, cohort, and case-control studies.
• Statistical analysis is used to interpret data and make informed conclusions about health risks.
• Public health policies and practices are shaped by the insights gained from epidemiological studies via risk factor identification.

Comparative Role of Public Health Professional and Epidemiologist

• Public Health Professional: Develops and implements programs promoting population/community health and well-being, using examples like national tobacco reduction campaigns.
• Epidemiologist: Studies disease patterns, causes, and effects to inform public health decisions, e.g. investigating cholera outbreaks.

Roles During the COVID-19 Outbreak

• Public Health Professional: Led the overall pandemic response by coordinating strategies locally, nationally, and globally, using examples such as developing public awareness campaigns, advising governments, and establishing vaccination infrastructure.
• Epidemiologist: Investigated the spread, patterns, factors of COVID-19 to provide evidence for control measures, analyzing infection rates, conducting contact tracing and studying vaccine effectiveness.

Distribution of Disease

• Person (who): Examines individual characteristics affecting illness likelihood, like age, sex, ethnicity, occupation, and behaviors.
• Time (when): Relates to the temporal distribution of diseases, including trends over time and seasonal variations.
• Place (where): Embraces the study of geographical distribution of diseases.

Morbidity

• Morbidity is any deviation (subject or objective) from a state of physiological or psychological well-being.
• Measures of morbidity frequency show the number of people newly becoming ill (incidence) or 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: 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. measles cases among children). Calculated as: (No. of new cases × 100,000) / Population at Risk

• Attack Rate: A specific incidence rate for a particular disease over a specific period of time, measuring the risk among those exposed to a certain exposure. Examples include food poisoning from contaminated food.

• Prevalence Rate: Total number of individuals with an attribute or disease at a particular time, divided by the population at risk of having the attribute or disease at that time. Calculated as: (Total number of cases with attribute or disease × 100,000) / Total Population at risk

• Relationship between Incidence and Prevalence: In a steady-state, stable population, Prevalence = Incidence × Duration of Disease

Study Designs

• Observational Studies: Researchers observe and record information without manipulating variables.
• Case Reports/Case Series: Detailed presentations of single or grouped patients with similar diagnoses.
• Cross-Sectional Studies: Assess outcomes or determinants of health in a population at a single point in time (e.g., prevalence of lung cancer among smokers).
• Case-Control Studies: Compare individuals with a disease (cases) to those without (controls) to identify risk factors retrospectively (e.g., comparing lung cancer smokers with non-smokers).
• Cohort Studies: Follow a group of people over time to see how their exposures affect outcomes (e.g., following smokers to assess lung cancer development).
• Experimental Studies: Involve intervention by the researcher, such as administering a treatment or behavioral change
  • Randomized Control Trials (RCTs): Participants randomly assigned to intervention or control groups.
  • Community Trials: Similar to RCTs but randomization units are communities or groups, not individuals.

Common Study Designs in Epidemiology (Continued)

• Ecological Studies: Examine relationships between exposure and disease at the group level, rather than individual level.
• Meta-Analyses: Combine data from multiple studies, increasing statistical power.

Importance of Study Designs

• Each design has strengths and weaknesses, chosen based on research question, ethical considerations, and practical constraints.
• RCTs are considered the gold standard for causality, but not always feasible or ethical.
• Observational studies are more common when RCTs aren't possible.
• Understanding designs is vital for interpreting epidemiological research and creating reliable public health data.

Determinants of Disease

• Determinants are factors influencing disease occurrence, from genetic to environmental.
• Determinants are categorized as:
  • Biological (genetics, age, sex)
  • Environmental (living conditions, climate, pollution)
  • Behavioral (lifestyle choices, dietary habits)
  • Social (socioeconomic status, community support networks)

Risk Factors

• Risk factors increase the likelihood of a person developing a disease or health problem. Examples are environmental, biological, behavioral, and social.
• Having risk factors doesn't guarantee disease; it increases the chances compared to individuals without them.

Some Examples of Risk Factors

• Biological: age, sex, genetics, ethnicity
• Environmental: exposure to pollutants, climate, living conditions
• Behavioral: smoking, alcohol consumption, diet, physical activity
• Socioeconomic: education level, income, occupational hazards

Types of Risk Factors

• Modifiable: Factors that can be changed (lifestyle habits like smoking, diet, exercise)
• Non-modifiable: Factors that cannot be changed (age, gender, genetic predisposition)

Measuring Risk

• Epidemiologists use incidence rates and prevalence proportions to quantify the risk associated with certain factors.

Causality

• Refers to the causative factors of a disease.
• Risk factors may increase likelihood, but do not guarantee causation.
• Establishing causality requires more research and evidence.

Interactions

• Multiple risk factors can interact to influence the likelihood of disease development.

Challenges in Epidemiology

• Data quality: Inaccurate/incomplete data leads to erroneous conclusions.
• Bias: Systematic errors in design/conduct of a study distort results.
• Confounding variables: Factors related to both exposure and outcome can mislead associations.
• Sample size: Small sample sizes may not represent the population well.