3. Epidemiology: Introduction

What is epidemiology?

The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems.

What are the six core components of epidemiology?

Study, Distribution, Determinants, Health-related states, Specified populations, Application.

What does "distribution" refer to in epidemiology?

The frequency and pattern of disease (who, where, and when).

What are determinants in epidemiology?

Causes, risk factors, and modes of transmission of disease.

Name six key uses of epidemiology.

Surveillance, outbreak investigation, identifying causes/risk factors, determining natural history, evaluating interventions, informing health policy.

What are the three components of the epidemiologic triad?

Host, Agent, Environment.

What are examples of host factors?

Age, genetics, immunity, behaviour.

What are examples of agent factors?

Biological, chemical, physical, nutritional agents.

What are examples of environmental factors?

Physical, social, and economic factors.

What additional components may be added to the epidemiologic triad?

Vector and reservoir.

What is a disease?

A pathological condition affecting the structure or function of an organism, characterized by specific signs, symptoms, or dysfunction.

List five characteristics of disease.

Abnormality, harm/disruption, specificity, aetiology, pathogenesis.

What are infectious diseases?

Diseases caused by pathogenic microorganisms.

What are genetic diseases?

Diseases caused by abnormalities in DNA.

What are metabolic diseases?

Diseases caused by dysfunction in biochemical processes.

What are degenerative diseases?

Diseases involving progressive deterioration of tissues or organs.

What are neoplastic diseases?

Diseases involving abnormal, uncontrolled cell growth.

What are autoimmune diseases?

Diseases in which the immune system attacks the body's own tissues.

What are mental disorders?

Disorders affecting thinking, emotion, and behaviour.

What is the natural history of disease?

The progression of disease over time without intervention.

What are the stages in the natural history of disease?

Susceptibility, Preclinical disease, Clinical disease, Recovery/Disability/Death.

What does incidence measure?

New cases of disease over a specified time period.

What is the incidence rate formula?

(New cases ÷ Person-time at risk) × K.

What is incidence mainly used for?

Identifying risk factors and causes of disease.

What does prevalence measure?

All existing cases (new and old) at a specific time.

What is point prevalence?

Existing cases at one point in time divided by the total population × K.

What is period prevalence?

All cases during a specified time period.

What is the relationship between prevalence and incidence?

Prevalence ≈ Incidence × Average duration of disease.

What is prevalence mainly used for?

Measuring disease burden and planning healthcare resources.

What is the crude death rate?

(Total deaths ÷ Population per year) × K.

What is the limitation of crude death rate?

It may be misleading when comparing populations with different age structures.

What is the age-specific mortality rate?

Deaths in a specific age group divided by the population of that age group × K.

What is the cause-specific mortality rate?

Deaths from a specific cause divided by the total population × K.

What is the case-fatality rate (CFR)?

Deaths from a disease divided by diagnosed cases × K.

What does the case-fatality rate measure?

Disease severity.

What is the formula for relative risk (RR)?

Incidence in exposed ÷ Incidence in unexposed.

What does RR = 1 mean?

No association.

What does RR > 1 mean?

Harmful association.

What does RR < 1 mean?

Protective association.

Which study design best calculates relative risk?

Cohort study.

What is attributable risk (AR)?

Incidence in exposed − Incidence in unexposed.

What does attributable risk measure?

Excess risk due to exposure.

What is an odds ratio (OR)?

An estimate of relative risk used mainly in case-control studies.

Which study design mainly uses the odds ratio?

Case-control study.

What are the three major categories of epidemiological study designs?

Descriptive, Analytical, Experimental.

What is the purpose of descriptive studies?

To describe disease patterns and generate hypotheses.

What questions do descriptive studies answer?

What, Who, Where, and When?

Name three types of descriptive studies.

Case reports/case series, Cross-sectional surveys, Ecological studies.

What is the purpose of analytical studies?

To test hypotheses about causes and risk factors.

What question do analytical studies answer?

Why is it happening?

What is the direction in a cohort study?

Exposure → Outcome.

What measures can cohort studies calculate?

Incidence and Relative Risk.

What are the two types of cohort studies?

Prospective and Retrospective.

What are cohort studies best for?

Studying multiple outcomes from one exposure and establishing temporal sequence.

What is the direction in a case-control study?

Outcome → Exposure.

Can case-control studies calculate incidence?

No.

What measure is used in case-control studies?

Odds Ratio.

What are case-control studies best for?

Rare diseases and diseases with long latency periods.

What are experimental studies?

Studies where investigators actively assign interventions to determine cause-effect relationships.

What is the gold standard experimental study?

Randomized Controlled Trial (RCT).

What is the primary goal of an RCT?

Establish causality.

Why is randomization important?

It balances known and unknown confounders.

What is bias?

A systematic error in study design, conduct, or analysis.

What is selection bias?

Bias due to how participants are selected.

What is information bias?

Bias due to how data are measured or collected.

What is confounding?

Distortion caused by a third variable associated with both exposure and outcome.

How can confounding be controlled?

Randomization, restriction, matching, stratification, multivariate analysis.

What is internal validity?

Whether study results are true for the study population.

What is external validity?

Whether results can be generalized to other populations.

What is public health surveillance?

Ongoing systematic collection, analysis, and interpretation of health data.

Name three types of surveillance.

Passive, Active, Syndromic.

What is passive surveillance?

Routine reports from healthcare providers.

What is active surveillance?

Health departments actively seek cases.

What is syndromic surveillance?

Surveillance based on symptoms before diagnosis.

What are the purposes of surveillance?

Detect outbreaks, monitor trends, evaluate programmes.

What are the first five outbreak investigation steps?

Prepare, confirm outbreak, verify diagnosis, construct case definition, find cases.

What are the last five outbreak investigation steps?

Perform descriptive epidemiology, develop hypotheses, test hypotheses, implement control measures, communicate findings.

What are the three levels of case definition?

Suspected, Probable, Confirmed.

What is a suspected case?

Meets initial clinical criteria with a plausible epidemiologic link but lacks confirmation.

What is a probable case?

Strong clinical and epidemiologic evidence without laboratory confirmation.

What is a confirmed case?

Laboratory-confirmed or meets definitive diagnostic criteria.

What is the epidemiologic flow from surveillance to intervention?

Surveillance → Descriptive data → Hypothesis → Analytical/Experimental testing → Causal inference → Public health intervention → Evaluation.