Epidemiology Overview and Approaches

Epidemiology Definition and Approach

• Epidemiology studies the distribution and determinants of health-related states or events in specified populations and the application of this study to control health problems.
• It looks at patterns of health and disease in populations and factors that influence those patterns.

Aims and Uses of Epidemiology

• Understanding the causes and risk factors of diseases: Identify what factors increase or decrease the likelihood of developing a disease.
• Monitoring the health of populations: Keep track of disease trends and patterns to identify potential public health threats.
• Evaluating the effectiveness of public health interventions: Measure the impact of programs designed to prevent or control disease.
• Developing public health policies: Provide evidence-based information for decision-making on public health programs and policies.

Variables in Epidemiology

• Person Variables: Attributes of individuals (e.g., age, sex, race, socioeconomic status) that can influence health.
• Place Variables: Geographic location and its characteristics (e.g., urban vs rural, environmental factors) that can influence health.
• Time Variables: Factors related to time (e.g., seasonality, trends over time) that can influence health.
• Exposure Variables: Factors that individuals are exposed to (e.g., lifestyle, biological, social factors) that can influence health.

Phases of Epidemiologic Approach

• Descriptive Epidemiology: Describes the distribution of disease in terms of person, place, and time.
• Analytical Epidemiology: Investigates the causes and risk factors for disease, seeking to establish associations between exposures and outcomes.
• Experimental Epidemiology: Involves controlled experiments to test the effectiveness of interventions.
• Evaluation Epidemiology: assesses the effectiveness of public health programs and interventions, focusing on how well they achieve their intended outcomes.

Types of Evaluation in Epidemiology

• Formative Evaluation: Evaluates programs during development or early implementation to identify potential issues and refine them.
• Process Evaluation: Monitors how programs are implemented and whether they reach the intended population.
• Outcome Evaluation: Measures the short-term effects of programs on the target population (e.g., changes in knowledge, behavior).
• Impact Evaluation: Examines the long-term overall effects of programs, including unintended consequences.

Surveillance

• Surveillance: The continuous, systematic collection, analysis, interpretation, and dissemination of health-related data for monitoring disease trends and identifying public health threats.

Methods of Surveillance

• Passive Surveillance: Relies on routine reporting of cases by healthcare providers, laboratories, or other sources without active solicitation.
• Active Surveillance: Involves public health authorities proactively seeking out cases by contacting healthcare providers or conducting surveys.
• Sentinel Surveillance: Utilizes a select group of healthcare providers or communities to monitor specific diseases and provide early warnings of outbreaks.
• Syndromic Surveillance: Monitors clusters of symptoms or syndromes rather than specific diagnoses to detect emerging health threats.
• Laboratory-Based Surveillance: Collapses and analyzes data from laboratory tests to monitor the prevalence of diseases.

Screening Tests

• Screening Tests: Tests performed on asymptomatic individuals to identify those at risk for a disease or condition.
• Purpose of Screening: Early detection of diseases to improve outcomes and facilitate timely intervention and treatment.

Validity of Screening Tests

• Validity: How well a test measures what it intends to measure.
• Sensitivity: The test correctly identifies those with the disease (true positives).
• Specificity: The test correctly identifies those without the disease (true negatives).
• Positive Predictive Value (PPV): The likelihood that a person with a positive test result actually has the disease.
• Negative Predictive Value (NPV): The likelihood that a person with a negative test result truly does not have the disease.

Reliability of Screening Tests

• Reliability: Consistency of a test when repeated under similar conditions.
• Test-Retest Reliability: Consistent results when the test is repeated on the same person under the same conditions.
• Inter-Observer Reliability: Consistent results when different healthcare professionals perform the test.
• Intra-Observer Reliability: Consistent results when the same healthcare provider repeats the test on the same patient.

Screening Programs

• Screening Programs: Systemic efforts to identify individuals in a population who may have a specific disease or condition, usually before symptoms appear.
• Goals of Screening Programs: Early detection to improve health outcomes by facilitating timely intervention, treatment, and management.

Criteria for Screening Programs

• Significant Public health Problem: the condition should be prevalent enough to justify a screening program.
• Early Detection Benefits: Early detection should improve treatment outcomes or reduce mortality.
• Accurate and Reliable test: The screening test should be valid (sensitive and specific) and reliable.
• Cost-Effectiveness: The benefits should outweigh the costs associated with the program.

Sources of Information for Disease Surveillance

• Census: A nationwide count of the population, providing demographic information.
• Vital Statistics (birth, death, marriage, divorce records): Data on major life events, providing insights into population trends.
• Morbidity Data: Information on illness, including incidence and prevalence of diseases.
• Mortality Data: Data on death rates, including causes of death.
• Notifiable Diseases Reports: Reports on diseases that must be reported to health authorities.
• Hospital Records: Data on hospital admissions, diagnoses, and procedures.
• Private Physicians’ Offices: Data on patient visits and diagnoses.
• Disease Registers: Systematic collection of information on specific diseases or conditions.
• Community Health Surveys: Data collected from individuals within a community.
• Research and Survey Findings: Data from epidemiological studies and surveys.
• Other Sources: Public health databases, social media monitoring, etc, providing additional information on health trends.