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West Nile Virus Activity --- United States, July 28--August 3, 2004

During July 28--August 3, a total of 141 cases of human West Nile virus (WNV) illness were reported from 11 states (Alabama, Arizona, California, Colorado, Florida, Illinois, Nevada, New York, North Dakota, South Dakota, and Texas). During 2004, a total of 20 states have reported a total of 406 cases of human WNV illness to CDC through ArboNET (Table, Figure). Of these, 247 (61%) were reported from Arizona. A total of 226 (57%) of the 406 cases occurred in males; the median age of patients was 51 years (range: 1 month--99 years). Illness onset ranged from April 20 to July 29; seven cases were fatal.

A total of 38 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET in 2004. Of these, 31 (82%) were reported from Arizona, two each from California and South Dakota, and one each from Colorado, Iowa, and New Mexico. Of the 38 PVDs, two persons aged 66 and 69 years subsequently had neuroinvasive illness, and seven persons (median age: 55 years [range: 22--72 years]) subsequently had West Nile fever.

In addition, during 2004, a total of 1,823 dead corvids and 223 other dead birds with WNV infection have been reported from 34 states. WNV infections in horses have been reported from 20 states (Alabama, Arizona, California, Colorado, Florida, Idaho, Iowa, Kentucky, Minnesota, Mississippi, Missouri, Nevada, North Carolina, Ohio, Oklahoma, South Dakota, Tennessee, Texas, Virginia, and Wyoming) and in a dog from New Mexico. WNV seroconversions have been reported in 253 sentinel chicken flocks from seven states (Arizona, California, Delaware, Florida, Louisiana, Nebraska, and Nevada) and in two wild hatchling birds from Ohio. Three seropositive sentinel horses were reported from Puerto Rico. A total of 1,486 WNV-positive mosquito pools have been reported from 24 states (Arizona, Arkansas, California, Colorado, Connecticut, Georgia, Illinois, Indiana, Kansas, Louisiana, Michigan, Mississippi, Missouri, Nebraska, Nevada, New Jersey, New Mexico, Ohio, Pennsylvania, South Dakota, Tennessee, Texas, Utah, and Virginia).

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


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