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Speaking Points
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•The top figure shows a typical epidemic curve from a Hepatitis A
outbreak, the bottom figure shows the epidemic curve from the anthrax attacks
that occurred during Fall 2001.
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•An epidemic curve is a histogram that shows the course of a disease
outbreak by plotting the number of cases by time of onset
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•You can often tell a great deal about the infectious agent and the
source of the infection from looking at an epidemic curve: if a disease is
transmitted person-to-person, you will likely have a wide epidemic curve as
people continue to become infected over time. A point-source infection will
likely result in a more narrow epidemic curve as people were likely all
exposed at the same time. If the infectious agent has a long incubation
period (the period of time between exposure and onset of symptoms) the
epidemic curve will likely be wider.
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•All of this information can assist in the process of investigating the
outbreak. An epidemic curve can help to identify a cluster of people who got
sick at the same time, and from there you can determine what those people had
in common. Once you identify a common event, for example, eating at a
particular restaurant, you can work backwards to figure out how long the
incubation period was. This information will make it easier to identify the
infectious agent.
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