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Confirming an Outbreak

Confirming the existence of an epidemic is not always straightforward. In part, that is because clear definitions of outbreak thresholds do not exist for all diseases. For some diseases, a single case may indicate an outbreak. These include cholera, measles, yellow fever, shigella, and the viral hemorrhagic fevers.

General guidelines for meningococcal meningitis are that for populations >30,000, 15 cases/100,000 persons/week in 1 week indicates an outbreak. However, with a high outbreak risk (i.e., no outbreak for 3+ years and vaccination coverage <80%), this threshold is reduced to 10 cases/100,000 persons/week. In populations <30,000, an incidence of 5 cases in 1 week or a doubling of cases over a 3-week period confirms an outbreak.

For malaria, an increase in the number of cases above what is expected for the time of year among a defined population in a defined area may indicate an outbreak.1

Post-Disaster Infectious Diseases

Following natural disasters, multiple factors increase the risk of contracting a communicable disease. These include inadequate sanitation, crowded conditions, food shortages, contaminated water, and inadequate immunization. Take all preventive measures possible and be alert for signs of potential epidemic diseases to avoid or quell a secondary disaster.

The diseases listed in Table 32-1 are common following disasters. All but tetanus have the potential of developing into epidemics. The best strategy is prevention, since adequate resources may not be available for treatment—or there may be no good treatment. Unfortunately, some preventive measures, such as hand washing, may not be easy to abide by in austere circumstances.

Table 32-1 Infectious Diseases Frequently Seen Post-Disaster

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