In a single-source outbreak, which pattern is most typical?

• A. Rapid rise in cases limited to those who share the exposure
• B. Gradual, multi-wave epidemic due to ongoing transmission
• C. Continuous new cases over long period with no peak
• D. No secondary cases occur

Answer: (A)

In a single-source (point-source) outbreak, cases cluster quickly because everyone who is exposed to the same contaminant or event tends to become ill within a similar incubation window. The epidemic curve rises rapidly to a sharp peak and then falls as the exposure ends and the exposed group passes through the incubation period. This creates a brief, intense surge of cases limited to those who shared the exposure.

This pattern differs from outbreaks driven by ongoing person-to-person transmission, which show gradual or multiple waves as the disease spreads through contacts. It also differs from continuous, long-lasting cases with no clear peak, which indicate ongoing exposure or endemic transmission rather than a single exposure event. While it’s possible for no secondary cases to occur, that would not define the typical single-source pattern, which is characterized by a rapid, short-lived rise among those exposed.