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West Nile Virus Activity --- United States, July 31--August 7, 2002, and Louisiana, January 1--August 7, 2002

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET and by states and other jurisdictions as of August 7, 2002.

United States

During the reporting period of July 31--August 7, a total of 68 laboratory-positive human cases of WNV-associated illness were reported from Louisiana (n=40), Mississippi (n=23), Texas (n=four), and Illinois (n=one). During the same period, WNV infections were reported in 447 dead crows, 263 other dead birds, 42 horses, and 183 mosquito pools.

During 2002, a total of 112 human cases with laboratory evidence of recent WNV infection have been reported from Louisiana (n=71), Mississippi (n=28), Texas (n=12), and Illinois (n=one). Five deaths have been reported, all from Louisiana. Among the 98 cases with available data, 59 (60%) occurred among men; the median age was 55 years (range: 3--88 years), and the dates of illness onset ranged from June 10 to July 29.

In addition, 1,076 dead crows and 827 other dead birds with WNV infection were reported from 34 states, New York City, and the District of Columbia (Figure 1); 87 WNV infections in horses have been reported from 12 states (Alabama, Florida, Georgia, Illinois, Kentucky, Louisiana, Minnesota, Mississippi, North Dakota, South Dakota, Tennessee, and Texas). During 2002, WNV seroconversions have been reported in 52 sentinel chicken flocks from Florida, Nebraska, and Pennsylvania; and 425 WNV-positive mosquito pools have been reported from 12 states (Alabama, Georgia, Illinois, Indiana, Massachusetts, Mississippi, New Jersey, Ohio, Pennsylvania, South Dakota, Texas, and Virginia), New York City, and the District of Columbia.


During January 1--August 7, Louisiana Office of Public Health (LOPH) has identified 71 laboratory-positive human cases of WNV. Clinically, 55 patients presented with WNV-associated meningoencephalitis (including five fatalities) and nine with WNV-associated fever. The clinical presentations of seven patients have not been ascertained.

Of the 71 cases, 38 (54%) occurred in males. Patients ranged in age from 13 to 88 years (median: 55 years). Decedents ranged in age from 53 to 83 years (median: 75 years). Patients resided in 13 different Louisiana parishes including the southeast (Ascension, East Baton Rouge, East Feliciana, Jefferson, Livingston, Orleans, St. Tammany, Tangipahoa, Washington, West Baton Rouge), southwest (Allen and Calcasieu), and north (Ouachita) regions of the state (Figure 2).

LOPH, with the assistance of CDC, has initiated a hospital-based, active surveillance system for viral encephalitis and meningitis. In addition, the incidence of WNV-associated fever in the community is being investigated through intensive evaluation of febrile patients with symptoms compatible with WNV-associated fever who consult physicians and hospitals. A clinical case-series has been established, and entomological and avian studies are under way.

Surveillance for WNV has been ongoing in Louisiana since spring 2000 and involves testing of dead birds, sick horses, mosquito pools, and sentinel chicken flocks. The increase in dead bird collections during the last week of May 2002 triggered the intensification of mosquito-control activities, including warnings to mosquito-control district staff and communities. The Louisiana Department of Health and Hospitals also created a website ( to provide the public with information about personal protective measures. A related media campaign was launched during the third week of June. Mosquito surveillance has guided vector-control activities, including larviciding of potential breeding sites and ultra-low volume applications of insecticide against adult mosquitoes.

Additional information about WNV activity is available at and

Figure 1

Figure 1
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Figure 2

Figure 2
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