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West Nile Virus Activity --- United States, September 22--28, 2004

During September 22--28, a total of 180 cases of human West Nile virus (WNV) illness were reported in the District of Columbia (DC) and 24 states (Alabama, Arizona, California, Georgia, Illinois, Iowa, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, Ohio, Pennsylvania, Texas, Utah, Wisconsin, and Wyoming).

During 2004, a total of 40 states have reported 1,784 cases of human WNV illness to CDC through ArboNET (Figure, Table). Of these, 563 (32%) cases were reported in California, 362 (20%) in Arizona, and 225 (13%) in Colorado. A total of 1,015 (58%) of the 1,752 cases for which such data were available occurred in males; the median age of patients was 51 years (range: 1 month--99 years). Illness onset ranged from April 23 to September 18; a total of 56 cases were fatal.

A total of 157 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET in 2004. Of these, 53 (34%) were reported in California; 37 (24%) in Arizona; 15 in Texas; 12 in New Mexico; five each in Colorado, Louisiana, and Nevada; four in Georgia; three each in Florida, Oklahoma, and South Dakota; two each in Minnesota, Missouri, and Wisconsin; and one each in Iowa, Michigan, Nebraska, New Jersey, North Dakota, and Pennsylvania. Of the 157 PVDs, three persons aged 35, 69, and 77 years subsequently had neuroinvasive illness, and 36 persons (median age: 53 years; range: 17--73 years) subsequently had West Nile fever.

In addition, during 2004, a total of 4,400 dead corvids and 1,054 other dead birds with WNV infection have been reported in 45 states and New York City. WNV infections have been reported in horses in 35 states, one bat in Wisconsin, five dogs in Nevada and New Mexico, three squirrels in Arizona, 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 858 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 6,156 WNV-positive mosquito pools have been reported in 34 states, DC, and New York City.

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


Table 2
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Figure 3
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