This cheat sheet provides a quick reference for key epidemiological concepts, outbreak investigation steps, study designs, and data interpretation methods. It includes definitions, formulas, and best practices for analyzing and controlling disease outbreaks. Ideal for Science Olympiad competitors, public health students, and epidemiology enthusiasts.
Epidemiology Basics
Epidemiology
- Study of disease distribution and determinants in populations.
- Aim: Identify causes, control disease, and prevent future outbreaks.
Key Terms
- Incidence Rate = (New cases / Population at risk) × 10⁵
- Prevalence Rate = (Total cases / Population) × 10⁵
- Mortality Rate = (Deaths / Population) × 10⁵
- Case Fatality Rate (CFR) = (Deaths from disease / Cases of disease) × 100%
- Attack Rate = (Cases in an outbreak / Total at risk) × 100%
Outbreak Investigation Steps
Step 1: Identify the Problem
- Verify the outbreak (higher cases than expected).
- Confirm the diagnosis.
Step 2: Define and Identify Cases
- Develop a case definition (person, place, time, clinical features).
- Classify cases: Confirmed, Probable, Possible.
Step 3: Collect and Analyze Data
- Use epidemic curves to determine outbreak pattern (point source, continuous, propagated).
- Identify common exposures (interviews, surveys).
Step 4: Develop Hypotheses
- Consider mode of transmission (foodborne, airborne, vector-borne).
- Compare affected vs. unaffected groups.
Step 5: Test Hypotheses
- Perform analytical epidemiology (case-control, cohort studies).
- Calculate relative risk (RR) and odds ratio (OR):
- RR = [A/(A+B)] / [C/(C+D)]
- OR = (A×D) / (B×C)
Step 6: Implement Control Measures
- Quarantine, vaccination, sanitation improvements.
- Public health education.
Step 7: Communicate Findings
- Report to public health officials.
- Publish in epidemiological bulletins.
Study Designs in Epidemiology
Descriptive Studies
- Case Report: Single patient description.
- Case Series: Group of similar cases.
- Cross-sectional Study: Snapshot of population at one time.
Analytical Studies
- Cohort Study: Follows exposed vs. unexposed groups over time.
- Measures Relative Risk (RR).
- Case-Control Study: Compares cases (diseased) vs. controls (healthy).
- Measures Odds Ratio (OR).
Experimental Studies
- Randomized Controlled Trial (RCT): Participants assigned to treatment vs. control.
- Field Trials: Testing interventions in real-world settings.
Epidemic Curves & Transmission Patterns
Epidemic Curve Types
- Point Source: Sudden spike, single exposure.
- Continuous Common Source: Cases rise and persist over time.
- Propagated: Multiple peaks, person-to-person spread.
Modes of Transmission
- Direct Contact: Person-to-person (e.g., flu, COVID-19).
- Indirect Contact: Contaminated objects (fomites).
- Vector-borne: Mosquitoes, ticks.
- Airborne: Droplets (e.g., tuberculosis, measles).
- Foodborne/Waterborne: Contaminated food/water (e.g., Salmonella, cholera).
Data Analysis & Interpretation
Measures of Association
- Relative Risk (RR) > 1: Exposure increases disease risk.
- Odds Ratio (OR) > 1: Cases have higher odds of exposure than controls.
Sensitivity vs. Specificity
- Sensitivity = True Positives / (True Positives + False Negatives).
- Specificity = True Negatives / (True Negatives + False Positives).
Bias in Epidemiology
- Selection Bias: Non-random sampling.
- Recall Bias: Errors in self-reported data.
- Confounding: Third variable affecting the exposure-disease relationship.
Tips and Sources
Useful Tips
- Always verify data accuracy before drawing conclusions.
- Use epidemic curves to visualize outbreak trends.
- Consider multiple hypotheses before ruling out causes.
- Communicate findings clearly to the public and health officials.