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Volume 14, Number 10—October 2008

Research

Ecologic Factors Associated with West Nile Virus Transmission, Northeastern United States

Heidi E. Brown1, James E. Childs, Maria A. Diuk-Wasser, and Durland FishComments to Author 
Author affiliations: Yale University, New Haven, Connecticut, USA;

Main Article

Table 2

Odds ratios for median split incidence of West Nile virus diseases in humans, for significant variables*

Predictor Adjusted
Unadjusted
OR (95% CI) Significance OR (95% CI) Significance
% Forest land use, per quartile
1st (<38.29) 4.40 (1.91–10.11) 0.000 4.36 (1.44–13.25) 0.009
2nd (38.29–56.56) 3.09 (1.38–6.92) 0.006 2.86 (1.01–8.06) 0.047
3rd (56.56–69.59) 0.84 (0.37–1.91) 0.675 0.81 (0.33–2.00) 0.644
4th (>69.59)
1
NA

1
NA
% Urban land use, per quartile
1st (<1.68) 1 NA 1 NA
2nd (1.68–4.66) 1.52 (0.68 - 3.39) 0.309 1.42 (0.54–3.76) 0.478
3rd (4.66–15.13) 2.44 (1.09 - 5.43) 0.030 3.08 (0.94–10.12) 0.064
4th (>15.13) 4.38 (1.91- 10.03) 0.000 7.02 (1.78–27.71) 0.031

*Variables categorized by percent of county classified as forested and percent of county classified as urban. Outcome categorized by median split to counties with low risk (incidence <0.75 cases/100,000 residents) and high risk (incidence >0.75 cases/100,000 residents). Overall trend is for increasing incidence with increasing measures of urbanization (for decreasing percentage forested land: χ2 = 9.47, df = 1, p< 0.01, goodness of fit χ2 = 3.50, df = 2,
p = 0.17; for increasing percentage urban land: χ2 = 7.13, df = 1, p< 0.01, goodness of fit χ2 = 1.98, df = 2, p = 0.37). Both unadjusted and surveillance bias and spatial relationship adjusted ORs are provided. OR, odds ratio; CI, confidence interval; NA, not applicable.

Main Article

1Current affiliation: University of Oxford, Oxford, UK.

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