Which scenario best illustrates a point source outbreak?

• A. A group exposed to a contaminated water source shows cases clustered in a short period with rapid decline.
• B. A citywide influenza outbreak with multiple waves over months.
• C. An outbreak with cases appearing weekly over months.
• D. Imported cases with no local cluster.

Answer: (A)

Point source outbreaks come from exposure to a single source over a brief period, producing a sharp, single peak in cases that rises quickly and then declines just as quickly. The scenario with a group exposed to a contaminated water source fits this pattern: cases occur clustered in a short time and then rapidly decline, reflecting one brief exposure event affecting many people.

In contrast, a citywide influenza outbreak with multiple waves over months shows a propagated pattern, where transmission spreads from person to person and new waves keep arising over time. An outbreak with cases appearing weekly over months suggests ongoing exposure or a continuing source, rather than a single brief exposure. Imported cases with no local cluster indicate sporadic, isolated events rather than a localized point source.