MSD Manual

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Epidemic curve, propagated source
Epidemic curve, propagated source

    Epidemic curve for a hypothetical propagated source outbreak in which cases can directly infect other cases separate from the initial source (eg, contagious disease). In a propagated source outbreak, individual-to-individual transmission occurs, often through several cycles before declining. The x-axis represents the day of onset of clinical signs and the y-axis represents the number of cases.

Courtesy of Dr. Donald L. Noah.