Choosing a Chart

• Line graph: trend over time
• Histogram / epi curve: frequency distribution
• Bar chart: compare categories
• Pie chart: parts of a whole
• Spot / area map: geography

Ratio vs. Proportion vs. Rate

• Ratio: any two values compared
• Proportion: numerator is part of denominator
• Rate: frequency over a span of time

Frequency Formulas

• Incidence proportion = new cases ÷ population at risk
• Incidence rate = new cases ÷ person-time observed
• Prevalence = all current cases ÷ total population
• Case-fatality rate = deaths ÷ people with disease

Breaking the Chain (Control)

1. Agent: treat / disinfect
2. Reservoir: treat carriers
3. Portal of exit: cover, dispose safely
4. Transmission: sanitation, vector control
5. Portal of entry: PPE, safe prep
6. Host: vaccinate, prophylaxis

Control → Elimination → Eradication → Extinction

• Control: reduced, needs upkeep
• Elimination: zero in one area
• Eradication: zero worldwide, forever
• Extinction: agent gone, even from labs

Food Safety & Herd Immunity

• Danger zone = 40°F to 140°F: bacteria multiply fastest
• Safe cook temps: poultry 165°F, ground beef 160°F
• Herd immunity threshold = 1 − 1/R₀ State/Nats

Levels of Prevention

1. Primordial: before risk exists
2. Primary: before exposure
3. Secondary: screen & treat early
4. Tertiary: treat active illness
5. Quaternary: avoid over-treatment