How do you differentiate a point source outbreak from a propagated outbreak based on the epidemic curve?

• A. Point source shows a sharp rise and fall; propagated pattern shows multiple waves over time with successive peaks.
• B. Point source shows multiple waves over time; propagated shows a sharp rise and fall.
• C. Point source shows a gradual rise; propagated shows no clear pattern.
• D. Point source shows a flat curve; propagated shows a single peak.

Answer: (A)

Epidemic curves reveal how transmission unfolds. A point source outbreak comes from a single exposure event, so cases cluster in a short time and the curve rises quickly and then falls just as fast, producing a single sharp peak. A propagated outbreak spreads through person-to-person transmission, so new generations of cases occur over time, creating several waves with successive peaks spaced by roughly the generation interval. As control measures or immunity reduce susceptible individuals, later waves may be smaller. That combination—a sharp rise and fall for a point source, versus multiple waves over time for a propagated outbreak—matches the described pattern.