Fig. 2.

(A) A common or point source outbreak characterized by a rapid increase and decrease of the epidemic curve over a short period. This pattern would be seen when there is a release of a biological agent that is nontransmissible at a single point in time in a single location. (B) (bar graph) A propagated source outbreak in which the disease is transmissible from 1 person to another. In this situation, particularly early in the outbreak, the number of cases does not increase in a linear fashion, but rather peaks and troughs associated with the natural transmission cycle (incubation period and infectious period) are seen. The line shows a steady increase in cases, which suggests an extended exposure to a source, as may be seen in a bioterrorism event (although it can occur naturally on occasion, although this is uncommon).

(Data from NATO Handbook on the Medical Aspects of NBC Defensive Operations, Part II–Biologic. Washington, DC: US Department of Defense, Department of the Army; 1996. Available at: http://www.fas.org/nuke/guide/usa/doctrine/dod/fm8-9/2toc.htm. Accessed January 23, 2013.)