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West Nile Virus Activity --- United States, October 13--19, 2004

During October 13--19, a total of 200 cases of human West Nile virus (WNV) illness were reported from 20 states (Arizona, Arkansas, California, Colorado, Illinois, Indiana, Iowa, Kansas, Maryland, Michigan, Mississippi, Missouri, Nevada, New Mexico, North Carolina, Oklahoma, Pennsylvania, South Dakota, Wisconsin, and Wyoming).

During 2004, a total of 40 states and the District of Columbia (DC) have reported 2,151 cases of human WNV illness to CDC through ArboNET (Table and Figure). Of these, 687 (32%) cases were reported in California, 378 (18%) in Arizona, and 276 (13%) in Colorado. A total of 1,232 (58%) of the 2,118 cases for which such data were available occurred in males; the median age of patients was 52 years (range: 1 month--99 years). Date of illness onset ranged from April 23 to October 6; a total of 68 cases were fatal.

A total of 191 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET in 2004. Of these, 70 (37%) were reported in California; 37 (19%) in Arizona; 16 in Texas; 15 in New Mexico; seven each in Colorado and Louisiana; six in Oklahoma; five in Nevada; four in Georgia; three each in Florida, Michigan, and South Dakota; two each in Minnesota, Mississippi, Missouri, and Wisconsin; and one each in Delaware, Iowa, Nebraska, New Jersey, North Dakota, Oregon, and Pennsylvania. Of the 191 PVDs, three persons aged 35, 69, and 77 years subsequently had neuroinvasive illness, and 45 persons (median age: 52 years; range: 17--73 years) subsequently had West Nile fever.

In addition, during 2004, a total of 5,073 dead corvids and 1,263 other dead birds with WNV infection have been reported from 45 states and New York City. WNV infections have been reported in horses in 36 states; one bat in Wisconsin; seven dogs in Nevada, New Mexico, and Wisconsin; six squirrels in Arizona and Wyoming; and 13 unidentified animal species in eight states (Arizona, Idaho, Illinois, Iowa, Missouri, Nevada, New York, and South Carolina). WNV seroconversions have been reported in 1,195 sentinel chicken flocks in 13 states (Alabama, Arizona, Arkansas, California, Delaware, Florida, Iowa, Louisiana, Nebraska, Nevada, Pennsylvania, South Dakota, and Utah) and in 25 wild hatchling birds in Missouri and Ohio. Four seropositive sentinel horses were reported in Minnesota and Puerto Rico. A total of 7,262 WNV-positive mosquito pools have been reported in 38 states, DC, and New York City.

Additional information about national WNV activity is available from CDC at and at


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