A propagated outbreak is characterized by which of the following?

• A. Cases occur over >1 incubation period with successive peaks reflecting increasing generations
• B. A single sharp peak and then no more cases
• C. Only a single exposure event
• D. No person-to-person transmission

Answer: (A)

Propagated outbreaks are driven by ongoing person-to-person transmission, so each new generation of infections seeds the next. Because the disease passes from one generation to the next, cases tend to appear over more than one incubation period and rise in successive waves, with peaks that reflect the timing of successive generations of transmission. This pattern—multiple waves of illness spaced by roughly the generation interval—is the hallmark of a propagated outbreak.

In contrast, a single sharp peak followed by no further cases indicates a point-source exposure confined to one event, not ongoing transmission. A scenario with only a single exposure event likewise produces a brief, isolated surge. And if there were no person-to-person transmission at all, you would not observe spread across generations or multiple peaks.