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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 20, 2005.

Thirty-eight states have reported 1,512 cases of human WNV illness in 2005 (Figure and Table 1). By comparison, in 2004, a total of 1,604 WNV cases had been reported as of September 21, 2004 (Table 2). A total of 780 (56%) of the 1,396 cases for which such data were available occurred in males; the median age of patients was 50 years (range: 3 months--98 years). Date of illness onset ranged from January 2 to September 16; a total of 41 cases were fatal.

A total of 268 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET during 2005. Of these, 84 were reported from California; 45 from Nebraska; 43 from Texas; 15 each from Louisiana and South Dakota; 12 from Arizona; nine from Kansas; eight from Iowa; six from Illinois; five from New Mexico; four each from Alabama and Minnesota; two each from Colorado, Michigan, Mississippi, Pennsylvania, and Utah; and one each from Idaho, Montana, Nevada, New York, North Carolina, North Dakota, Ohio, and Oregon. Of the 268 PVDs, two persons aged 53 and 56 years subsequently had neuroinvasive illness; three persons aged 17, 41 and 51 years subsequently had other illnesses; and 61 persons (median age: 47 years [range: 17--78 years]) subsequently had West Nile fever.

In addition, 3,228 dead corvids and 698 other dead birds with WNV infection have been reported from 41 states. WNV infections have been reported in horses from 29 states, four dogs from Idaho, Minnesota, and Nebraska, four squirrels from Arizona, and two unidentified animal species in two states (Arizona and Illinois). WNV seroconversions have been reported in 845 sentinel chicken flocks from 12 states. One seropositive sentinel horse was reported from Minnesota. A total of 9,318 WNV-positive mosquito pools have been reported from 38 states (Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, Washington, and Wisconsin) 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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