Update on West Nile virus activity

Author: Carrie Morantz, Brian Torrey
Date: March 15, 2003

West Nile virus (WNV) activity expanded substantially in the United States last year, with the number of reported human infections increasing more than 20-fold from the previous three years, according to provisional data from the Centers for Disease Control and Prevention (CDC). The report, "Provisional Surveillance Summary of the West Nile Virus Epidemic--United States, January-November 2002," is available online at www.cdc.gov/mmwr/preview/mmwrhtml/mm5150a1.htm.

In 2002, there were 3,389 human cases of WNV-associated illness reported, compared with 149 cases reported between 1999 and 2001. West Nile meningoencephalitis (69 percent of WNV cases) was the most common illness, followed by West Nile fever (21 percent), and unspecified illness (10 percent). Onset of illness ranged from June 10 to November 4, and the epidemic peak occurred during the week that ended August 24.

WNV activity was reported in 44 states and the District of Columbia in 2002, compared with 27 states and the District of Columbia in 2001. Nearly two thirds of the WNV infections that affected humans last year were reported in Illinois, Michigan, Ohio, Louisiana, and Indiana.

The median age of persons infected with WNV was 55 years. Of the 2,354 persons with West Nile meningoencephalitis last year, 199 (9 percent) died; two (0.3 percent) persons with West Nile fever died.

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