who were exposed to the suspected
risk factor with the cumulative incidence
of those who were not exposed.
Investigators’ conclusions based on
the weight of the accumulated evidence
are then written up in a report.
Control measures need to be applied
as soon as possible after an outbreak
begins to minimize the number of
victims.
An outbreak investigation may be
initiated by an analytic study. In the
Iowa trichinosis example, a case-control
study enabled the investigators to
ascertain which of three social events
was the source of the contaminated
pork whose consumption triggered
the outbreak.
Clusters of noninfectious health
events, including youth suicides,
childhood leukemias, and birth defects,
sometimes occur in local communities.
CDC defines a cluster as “an
unusual aggregation, real or perceived,
of health events that are
grouped together in time and space
and that are reported to a health
agency.”
5 CDC has developed a series
of specific guidelines to help health
officials manage and investigate disease
and injury clusters.