West Nile virus infection in the United States: A review and update

In August 1999, a cluster of patients were admitted to medical ICUs in New York City with fever, confusion, GI complaints, muscle weakness, and a presumed diagnosis of encephalitis. A cooperative investigation was conducted by the city and state departments of health along with the CDC and ultimately determined that West Nile virus (WNV) was the causative agent; interagency cooperation was key in identifying the outbreak. It was the first time that WNV was found in the Western Hemisphere. In the following 2 years, cases appeared in areas near New York and then in states up and down the East Coast. The epidemiology this year will depend on weather and other factors.