Dead bird clusters as an early warning system for West Nile virus activity

Abstract

An early warning system for West Nile virus (WNV) outbreaks could provide a basis for targeted public education and surveillance activities as well as more timely larval and adult mosquito control. We adapted the spatial scan statistic for prospective detection of infectious disease outbreaks, applied the results to data on dead birds reported from New York City in 2000, and reviewed its utility in providing an early warning of WNV activity in 2001. Prospective geographic cluster analysis of dead bird reports may provide early warning of increasing viral activity in birds and mosquitoes, allowing jurisdictions to triage limited mosquito-collection and laboratory resources and more effectively prevent human disease caused by the virus. This adaptation of the scan statistic could also be useful in other infectious disease surveillance systems, including those for bioterrorism.

Figure 1

Dead bird cluster surveillance system. SAS, SAS statistical package (SAS Institute, Inc., Cary, NC); ESRI, Environmental Systems Research Institute; SQL, structured query language.

Figure 2

Dead bird clusters, West Nile virus (WNV)-positive dead birds, human cases, and mosquito traps, New York City, 2000. The shading represents the cumulative frequency of dead bird clusters in each census tract as of the date of analysis. Cumulative WNV-positive birds and mosquitoes are displayed on the basis of their date of collection; human cases are shown on the basis of their date of onset of illness.

Figure 3

Dead bird clusters, West Nile virus (WNV)-positive dead birds, human cases, and mosquito traps, New York City, 2001. The shading represents the cumulative frequency of dead bird clusters in each census tract as of the date of analysis. Cumulative WNV-positive birds and mosquitoes are displayed on the basis of their date of collection; human cases are shown on the basis of their date of onset of illness.