In addition, the density of dead bird reports is confounded by the background bird population, human population density, and the varying propensity of different communities to report dead birds. However, county-level analysis is insensitive to small-area clustering. The county-level density of dead bird ( 4) and crow ( 5) reports per square mile was also strongly correlated with levels of WNV activity in 2000. However, mosquito and bird collection and laboratory testing are costly and resource intensive. Retrospective county-level analysis of year 2000 data showed that dead birds and mosquito pools with laboratory evidence of WNV were collected in the outbreak epicenter, Staten Island, approximately 2 weeks before onset of the first human case ( 4). In the summer of 2000, the New York City Department of Health and Mental Hygiene established an unprecedented citywide network of adult mosquito traps, sentinel bird flocks, and system for reporting, collecting, and testing dead birds.
Since the 1999 WNV outbreak in New York City, which caused thousands of human infections ( 2) and 59 severe meningoencephalitis cases ( 3) including 7 deaths, health officials have been searching for an early warning system that could help prevent human illness and deaths. By the end of 2002, West Nile virus (WNV) activity had been reported in all but four of the lower continental states, with >3,500 human cases reported ( 1).
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