- Full (HTML) - Full (PDF) - Related EHP Articles - PubMed:Related Articles - PubMed:Citation - Cited in PMC -

Jonathan E. Soverow,^1,2 Gregory A. Wellenius,² David N. Fisman,³ and Murray A. Mittleman^2,4

¹New York University School of Medicine, New York, New York, USA; ²Cardiovascular Epidemiology Research Unit, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA; ³Hospital for Sick Children, Toronto, Ontario, Canada; ⁴Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA

Abstract
Background: The effects of weather on West Nile virus (WNV) mosquito populations in the United States have been widely reported, but few studies assess their overall impact on transmission to humans.

Objectives: We investigated meteorologic conditions associated with reported human WNV cases in the United States.

Methods: We conducted a case–crossover study to assess 16,298 human WNV cases reported to the Centers for Disease Control and Prevention from 2001 to 2005. The primary outcome measures were the incidence rate ratio of disease occurrence associated with mean weekly maximum temperature, cumulative weekly temperature, mean weekly dew point temperature, cumulative weekly precipitation, and the presence of ≥ 1 day of heavy rainfall (≥ 50 mm) during the month prior to symptom onset.

Results: Increasing weekly maximum temperature and weekly cumulative temperature were similarly and significantly associated with a 35–83% higher incidence of reported WNV infection over the next month. An increase in mean weekly dew point temperature was significantly associated with a 9–38% higher incidence over the subsequent 3 weeks. The presence of at least 1 day of heavy rainfall within a week was associated with a 29–66% higher incidence during the same week and over the subsequent 2 weeks. A 20-mm increase in cumulative weekly precipitation was significantly associated with a 4–8% increase in incidence of reported WNV infection over the subsequent 2 weeks.

Conclusions: Warmer temperatures, elevated humidity, and heavy precipitation increased the rate of human WNV infection in the United States independent of season and each others’ effects.

Key words: case–crossover study, climate change, global warming, mosquito, vector-borne illness, weather, West Nile virus. Environ Health Perspect 117:1049–1052 (2009) . doi:10.1289/ehp.0800487 available via http://dx.doi.org/ [Online 16 March 2009]

Address correspondence to M.A. Mittleman, Cardiovascular Epidemiology Research Unit, Department of Medicine, Beth Israel Deaconess Medical Center, 330 Brookline Ave., MASCO 442, Boston, MA 02215. Fax: (617) 632-7698. E-mail: mmittlem@bidmc.harvard.edu

We thank the Centers for Disease Control and Prevention, Division of Vector-Borne Infectious Diseases, for making the case data available.

This project was supported by grants P01-ES009825, F32-ES013804, and K99-ES015774 from the National Institute of Environmental Health Sciences (NIEHS) .

The views expressed in this article are solely the responsibility of the authors and do not necessarily represent the official views of the NIEHS or any of the institutional affiliations listed. The NIEHS had no role in the design and conduct of the study ; the collection, management, analysis, and interpretation of the data ; or the preparation, review, or approval of the manuscript. J.E.S., G.A.W., and M.A.M. had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

The authors declare they have no competing financial interests.

Received 14 December 2008 ; accepted 16 March 2009.