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West Nile Virus Activity --- United States, October 16--22, 2003

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m., Mountain Daylight Time, October 22, 2003.

During the reporting week of October 16--22, a total of 429 human cases of WNV infection were reported from 26 states (Alabama, Arizona, Arkansas, California, Georgia, Illinois, Kansas, Maryland, Massachusetts, Michigan, Minnesota, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Dakota, Tennessee, Texas, Vermont, and Virginia), including seven fatal cases from four states (Maryland, Nebraska, New York, and Texas). During the same period, WNV infections were reported in 281 dead birds, 246 mosquito pools, 183 horses, 2 dogs, 2 squirrels, and one unidentified animal species.

During 2003, a total of 7,386 human cases of WNV infection have been reported from Colorado (n = 2,170), Nebraska (n = 1,359), South Dakota (n = 955), Texas (n = 457), North Dakota (n = 375), Wyoming (n = 320), Montana (n = 216), Pennsylvania (n = 202), New Mexico (n = 194), Minnesota (n = 136), Iowa (n = 128), Ohio (n =86), Louisiana (n = 84), Kansas (n = 78), Oklahoma (n = 59), Mississippi (n = 56), New York (n = 56), Illinois (n = 45), Maryland (n = 45), Missouri (n = 43), Florida (n = 32), Georgia (n = 31), Alabama (n = 30), Indiana (n = 30), New Jersey (n = 26), Arkansas (n = 21), North Carolina (n = 21), Tennessee (n = 19), Virginia (n = 18), Massachusetts (n = 16), Delaware (n = 13), Kentucky (n = 13), Wisconsin (n = 13), Connecticut (n = 12), Michigan (n = six), Rhode Island (n = five), District of Columbia (n = three), Arizona (n = two), California (n = two), Nevada (n = two), New Hampshire (n = two), Vermont (n = two), South Carolina (n = one), Utah (n = one), and West Virginia (n = one) (Figure). Of 7,269 (98%) cases for which demographic data were available, 3,841 (53%) occurred among males; the median age was 47 years (range: 1 month--99 years), and the dates of illness onset ranged from March 28 to October 10. Of the 7,269 cases, 155 fatal cases were reported from Colorado (n = 44), Texas (n = 17), Nebraska (n = 16), New York (n = eight), South Dakota (n = eight), Wyoming (n = eight), Pennsylvania (n = six), Maryland (n = five), Georgia (n = four), Iowa (n = four), Minnesota (n = four), New Mexico (n = four), North Dakota (n = four), Alabama (n = three), Ohio (n = three), Indiana (n = two), Missouri (n = two), Montana (n = two), New Jersey (n = two), Delaware (n = one), Illinois (n = one), Kansas (n = one), Kentucky (n = one), Louisiana (n = one), Michigan (n = one), Mississippi (n = one), Tennessee (n = one), and Virginia (n = one). A total of 682 presumptive West Nile viremic blood donors have been reported to ArboNET. Of these, 596 (87%) were reported from the following nine western and midwestern states: Colorado, Kansas, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, and Wyoming. Of the 529 donors for whom data were reported completely, six subsequently had meningoencephalitis, and 76 subsequently had West Nile fever.

In addition, 10,453 dead birds with WNV infection have been reported from 42 states, the District of Columbia, and New York City; 3,270 WNV infections in horses, 16 WNV infections in dogs, 14 infections in squirrels, and 24 infections in unidentified animal species have been reported from 39 states. During 2003, WNV seroconversions have been reported in 1,246 sentinel chicken flocks from 15 states. Of the 46 seropositive sentinel horses reported, Illinois reported 35; Minnesota, seven; South Dakota, three; and West Virginia, one. In addition, seropositivity was reported from one other unidentified animal species. A total of 6,667 WNV-positive mosquito pools have been reported from 38 states, the District of Columbia, and New York City.

Additional information about WNV activity is available from CDC at and


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