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Update: West Nile Virus Activity --- United States, 2005

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, October 25, 2005.

Forty-two states have reported 2,435 cases of human WNV illness in 2005 (Figure and Table 1). By comparison, a total of 2,231 WNV cases had been reported as of October 26, 2004 (Table 2). A total of 1,284 (56%) of the 2,282 cases for which such data were available in 2005 occurred in males; the median age of patients was 51 years (range: 3 months--98 years). Dates of illness onset ranged from January 2 to October 14; a total of 73 cases were fatal.

A total of 372 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET during 2005. Of these, 85 were reported from California; 57 from Nebraska; 54 from Texas; 22 from Louisiana; 20 from Arizona; 19 from Kansas; 17 from Iowa; 16 from South Dakota; 12 from Oklahoma; 11 from Minnesota; 10 from Illinois; five each from Michigan, New Mexico, and North Dakota; four each from Alabama, Pennsylvania, and Utah; three each from Nevada and Wisconsin; two each from Colorado, Indiana, Mississippi, Montana, and Ohio; and one each from Idaho, Kentucky, Missouri, New York, North Carolina, and Oregon. Of the 372 PVDs, three persons aged 53, 56, and 72 years subsequently had neuroinvasive illness; seven persons (median age: 41 years [range: 17--64 years]) subsequently had other illnesses; and 78 persons (median age: 46 years [range: 17--78 years]) subsequently had West Nile fever.

In addition, 3,988 dead corvids and 845 other dead birds with WNV infection have been reported from 45 states. WNV infections have been reported in horses in 32 states; five dogs in Idaho, Minnesota, and Nebraska; six squirrels in Arizona; and five unidentified animal species in four states (Arizona, Illinois, North Carolina, and Texas). WNV seroconversions have been reported in 1,200 sentinel chicken flocks from 16 states. Eight seropositive sentinel birds have been reported in Michigan. One seropositive sentinel horse was reported in Minnesota. A total of 10,787 WNV-positive mosquito pools have been reported from 41 states and the District of Columbia.

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


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Table 1

Table 1
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Table 2

Table 2
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