West Nile Virus Infection May Be Greater Than Previously Thought
West Nile virus was recognized in the Western Hemisphere for the first time in 1999, when it caused an epidemic of encephalitis and meningitis in New York City. Intensive hospital-based, public health surveillance registered seven deaths in the region from meningoencephalitis (inflammation of the brain and spinal cord).
A detailed analysis of the New York City outbreak suggests that a substantial--and previously undiagnosed--number of West Nile fever cases accompanied the 59 cases of potentially deadly West Nile meningoencephalitis seen during the outbreak, researchers say.
West Nile virus was first isolated in the West Nile District of Uganda in 1937. According to the Centers for Disease Control and Prevention (CDC), most infections are mild with symptoms such as fever, headache, and body aches. People older than 50 are at highest risk of severe disease, which may result in a number of symptoms, including high fever, disorientation, muscle weakness, and, rarely, death.
The New York City Department of Health and the CDC conducted a household-based survey in October 1999, about six weeks after the outbreak in New York. Investigators used a representative sample of households in an area surrounding the center of the outbreak. Blood samples were taken and tested for antibodies specific for the West Nile virus.
The study, published in the July 28, 2001, issue of The Lancet, concluded that for every diagnosed case of meningoencephalitis, there were likely to be 140 other infections, including 30 individuals with an influenza-like illness. …