The Epidemiologic Approach

1. Count cases by time, place, person
2. Divide by the population at risk → rate
3. Compare the rate across time/groups

6 Core Functions of Epidemiology

1. Surveillance
2. Field investigation
3. Analytic studies
4. Evaluation
5. Linkages
6. Policy development

5-Step Surveillance Process

1. Identify & define the problem
2. Collect data
3. Analyze & interpret
4. Disseminate findings
5. Evaluate & act (repeat)

4 Types of Surveillance

• Passive: providers report on their own
• Active: health dept. asks for reports
• Sentinel: a fixed reporting network
• Syndromic: tracks symptoms/proxies

Disease Frequency, Low → High

1. Sporadic (occasional, no pattern)
2. Endemic (constant baseline)
3. Hyperendemic (persistently high)
4. Outbreak / Epidemic (above expected)
5. Pandemic (multi-continent)

Natural History Timeline

1. Exposure
2. Incubation / latency
3. Onset of symptoms
4. Clinical disease
5. Recovery, disability, or death