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West Nile Virus Activity --- United States, September 25--October 1, 2003

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m., Mountain Daylight Time, October 1, 2003.

During the reporting week of September 25--October 1, a total of 1,034 human cases of WNV infection were reported from 27 states (Colorado, Connecticut, Georgia, Illinois, Iowa, Kansas, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Vermont, Virginia, and Wyoming), including 22 fatal cases from 10 states (Colorado, Georgia, Maryland, Michigan, Montana, Nebraska, New York, Pennsylvania, Texas, and Wyoming). During the same period, WNV infections were reported in 692 mosquito pools, 549 dead birds, 306 horses, four squirrels, two unidentified animal species, and one dog.

During 2003, a total of 5,861 human cases of WNV infection have been reported from Colorado (n = 1,991), Nebraska (n = 999), South Dakota (n = 840), Texas (n = 335), Wyoming (n = 313), Montana (n = 207), New Mexico (n = 174), North Dakota (n = 148), Iowa (n = 98), Minnesota (n = 96), Pennsylvania (n = 91), Louisiana (n = 67), Ohio (n = 57), Mississippi (n = 51), New York (n = 45), Oklahoma (n = 40), Kansas (n = 40), Missouri (n = 38), Florida (n = 32), Alabama (n = 26), Illinois (n = 22), Maryland (n = 20), North Carolina (n = 19), New Jersey (n = 17), Georgia (n = 13), Arkansas (n = 11), Massachusetts (n = 10), Wisconsin (n = 10), Connecticut (n = nine), Tennessee (n = eight), Virginia (n = seven), Indiana (n = six), Kentucky (n = six), Delaware (n = four), Rhode Island (n = three), New Hampshire (n = two), Arizona (n = one), Michigan (n = one), Nevada (n = one), South Carolina (n = one), Utah (n = one), and Vermont (n = one) (Figure). Of 5,787 (99%) cases for which demographic data were available, 3,028 (52%) 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 September 26. Of the 5,787 cases, 115 fatal cases were reported from Colorado (n = 36), Nebraska (n = 15), Texas (n = 11), South Dakota (n = eight), Wyoming (n = eight), New York (n = six), New Mexico (n = four), Alabama (n = three), Iowa (n = three), Minnesota (n = three), Ohio (n = three), Georgia (n = two), Maryland (n = two), Missouri (n = two), Montana (n = two), Kansas (n = one), Louisiana (n = one), Michigan (n = one), Mississippi (n = one), New Jersey (n = one), North Dakota (n = one), and Pennsylvania (n = one). A total of 617 presumptive West Nile viremic blood donors have been reported to ArboNET. Of these, 558 (90%) 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 489 donors for whom data was completely reported, four subsequently had meningoencephalitis, and 66 subsequently had West Nile fever. In addition, 8,955 dead birds with WNV infection were reported from 42 states, the District of Columbia, and New York City; 2,449 WNV infections in horses have been reported from 36 states, 19 infections in unidentified animal species, 13 infections in dogs, and nine infections in squirrels. During 2003, WNV seroconversions have been reported in 612 sentinel chicken flocks from 13 states. Of the eight seropositive sentinel horses reported, Minnesota reported four; South Dakota, three; and West Virginia, one. A total of 5,633 WNV-positive mosquito pools have been reported from 39 states and New York City.

Additional information about WNV activity is available from CDC at and


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