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West Nile Virus Activity --- United States, August 25--31, 2004

During August 25--31, a total of 210 cases of human West Nile virus (WNV) illness were reported from 14 states (Arizona, California, Florida, Illinois, Indiana, Kansas, Maryland, Minnesota, Montana, Nevada, New Mexico, North Dakota, Oklahoma, and Pennsylvania).

During 2004, a total of 36 states have reported 1,053 cases of human WNV illness to CDC through ArboNET (Table, Figure). Of these, 326 (31%) cases were reported from California, 316 (30%) cases were reported from Arizona, and 141 (13%) cases were reported from Colorado. A total of 588 (56%) of the 1,053 cases occurred in males; the median age of patients was 51 years (range: 1 month--99 years). Illness onset ranged from April 23 to August 24; a total of 28 cases were fatal.

A total of 85 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET in 2004. Of these, 36 (42%) were reported from Arizona, 20 from California, eight from New Mexico, six from Texas, three each from Florida and South Dakota, two from Colorado and Wisconsin, and one each from Illinois, Iowa, Louisiana, Minnesota, and Missouri . Of the 85 PVDs, three persons aged 42, 66 and 69 years subsequently had neuroinvasive illness, and 15 persons (median age: 55 years; range: 17--73 years) subsequently had West Nile fever.

In addition, during 2004, a total of 3,307 dead corvids and 671 other dead birds with WNV infection have been reported from 44 states. WNV infections have been reported in horses from 31 states (Alabama, Arizona, Arkansas, California, Colorado, Florida, Georgia, Idaho, Illinois, Iowa, Kansas, Kentucky, Michigan, Minnesota, Mississippi, Missouri, Montana, Nevada, New Mexico, North Carolina, Ohio, Oklahoma, Oregon, South Dakota, Tennessee, Texas, Utah, Virginia, Wisconsin, West Virginia, and Wyoming) and in five dogs from Nevada and New Mexico. Three unidentified animal species with WNV infection were reported from Illinois, Iowa, and Nevada. WNV seroconversions have been reported in 571 sentinel chicken flocks from 11 states (Arizona, Arkansas, California, Delaware, Florida, Iowa, Louisiana, Nebraska, Nevada, South Dakota, and Utah) and in two wild hatchling birds from Ohio. Three seropositive sentinel horses were reported from Puerto Rico. A total of 4,024 WNV-positive mosquito pools have been reported from 31 states (Arizona, Arkansas, California, Colorado, Connecticut, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Mississippi, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, Ohio, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Virginia, and Wisconsin).

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


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