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West Nile Virus Activity --- United States, September 15--21, 2004

During September 15--21, a total of 218 cases of human West Nile virus (WNV) illness were reported from 21 states (Arizona, California, Florida, Illinois, Indiana, Kansas, Maryland, Michigan, Minnesota, Mississippi, Missouri, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, Utah, Wisconsin, and Wyoming).

During 2004, a total of 39 states have reported 1,604 cases of human WNV illness to CDC through ArboNET (Table, Figure). Of these, 507 (32%) cases were reported from California, 355 (22%) from Arizona, and 225 (14%) from Colorado. A total of 897 (58%) of the 1,541 cases for which all 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 14; a total of 48 cases were fatal.

A total of 143 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET in 2004. Of these, 51 (36%) were reported from California; 37 (26%) from Arizona; 15 from Texas; 12 from New Mexico; five from Colorado; four from Georgia; three each from Florida, Oklahoma, and South Dakota; two each from Missouri and Wisconsin; and one each from Iowa, Louisiana, Minnesota, Nebraska, North Dakota, and Pennsylvania. Of the 143 PVDs, three persons aged 35, 69, and 77 years subsequently had neuroinvasive illness, and 32 persons (median age: 55 years; range: 17--73 years) subsequently had West Nile fever.

In addition, during 2004, a total of 4,188 dead corvids and 987 other dead birds with WNV infection have been reported from 44 states and New York City. WNV infections have been reported in horses from 34 states (Alabama, Arizona, Arkansas, California, Colorado, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Mississippi, Missouri, Montana, Nevada, New Jersey, New Mexico, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Virginia, Wisconsin, West Virginia, and Wyoming) and in five dogs from Nevada and New Mexico. Three squirrels with WNV infection were reported from Arizona. Six unidentified animal species with WNV infection were reported from Arizona, Idaho, Illinois, Iowa, Missouri, and Nevada. WNV seroconversions have been reported in 799 sentinel chicken flocks from 13 states (Alabama, Arizona, Arkansas, California, Delaware, Florida, Iowa, Louisiana, Nebraska, Nevada, Pennsylvania, South Dakota, and Utah) and in seven wild hatchling birds from Missouri and Ohio. Three seropositive sentinel horses were reported from Puerto Rico. A total of 5,707 WNV-positive mosquito pools have been reported from 34 states and New York City.

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


Table 1
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Figure 1
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