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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, September 6, 2005.

Thirty-two states have reported 821 cases of human WNV illness in 2005 (Figure and Table 1). By comparison, in 2004, a total of 1,191 WNV cases had been reported as of September 7, 2004 (Table 2). A total of 432 (56%) of the 772 cases for which such data were available occurred in males; the median age of patients was 50 years (range: 3 months--92 years). Date of illness onset ranged from January 2 to August 31; a total of 18 cases were fatal.

A total of 163 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET during 2005. Of these, 49 were reported from California; 32 from Texas; 22 from Nebraska; 14 from South Dakota; 10 from Louisiana; six from Arizona; five from Illinois; four each from Kansas and Minnesota; three from Iowa; two each from Alabama, Colorado, Mississippi, and New Mexico; and one each from Michigan, Nevada, North Carolina, North Dakota, Pennsylvania, and Utah. Of the 163 PVDs, three persons aged 53, 56, and 71 years subsequently had neuroinvasive illness; three persons aged 17, 41, and 51 years subsequently had other illnesses; and 38 persons (median age: 47 years [range: 17--77 years]) subsequently had West Nile fever.

In addition, 2,381 dead corvids and 507 other dead birds with WNV infection have been reported from 38 states. WNV infections have been reported in horses from 28 states, three dogs from Minnesota and Nebraska, four squirrels from Arizona, and two unidentified animal species in two states (Arizona and Illinois). WNV seroconversions have been reported in 549 sentinel chicken flocks from 11 states. One seropositive sentinel horse was reported from Minnesota. A total of 6,833 WNV-positive mosquito pools have been reported from 36 states (Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, 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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Table 1

Table 1
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Table 2

Table 2
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