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Geographic prediction of human cases of West Nile Virus in New York State using dead crow clusters

Glen D. Johnson, Zoonoses Program, New York State Department of Health, 621 Corning Tower, Empire State Plaza, Albany, NY 12237, 518-474-3186, gdj01@health.state.ny.us

The risk of a human case of West Nile Virus (WNV) in New York State, excluding New York City, for the year 2002, was estimated for individuals whose town of residence was proximal to spatial clusters of dead American Crows (Corvus brachyrhynchos), a sentinel for WNV. For each week of the WNV season, clusters were separately delineated by the binomial spatial scan statistic and kernel density smoothing. Town-level exposure was defined spatially as being within one mile of a cluster and temporally according to multiple criteria. The risk of a human case occurring in exposed towns, relative to unexposed towns, was estimated by two approaches: 1) Poisson regression, adjusting for week and geographic region, and 2) Cox proportional hazards modeling, where the week of a human case was treated as the failure time and baseline hazard was stratified by region. Both methods estimated relative risks of around 2 to 3 (P < 0.05) for several exposure definitions. Of these, the highest risks were for towns spatially associated with kernel density clusters and for towns temporally associated with a cluster 0, 1 or 2 weeks prior to a human case. Relative risks for exposure according to these criteria are 2.83 (95% CI = 1.45, 5.53) from Poisson regression and 3.27 (95% CI = 1.56, 6.89) from proportional hazards regression, after adjusting for town population density as a confounder. These results are relevant to spatial-temporal surveillance for zoonotic diseases in general, including those of bioterrorism concern.

Learning Objectives: At the conclusion of this presentation, the participant should be able to

Presenting author's disclosure statement:
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.

Information and GIS Systems for Public Health Practice

The 132nd Annual Meeting (November 6-10, 2004) of APHA