Environmental and social determinants of human risk during a West Nile virus outbreak in the greater Chicago area, 2002

Marilyn O Ruiz¹ , Carmen Tedesco² , Thomas J McTighe¹ , Connie Austin³ and Uriel Kitron¹

¹Department of Veterinary Pathobiology, University of Illinois, 2001 South Lincoln Ave, Urbana, IL, USA

²Department of Geography, University of Illinois, 607 S. Matthews Ave, Urbana, IL, USA

³Illinois Department of Public Health, 535 W. Jefferson St, Springfield, IL, USA

author email corresponding author email

International Journal of Health Geographics 2004, 3:8doi:10.1186/1476-072X-3-8


Published:	20 April 2004

Abstract

Background

The outbreak of West Nile Virus (WNV) in and around Chicago in 2002 included over 680 cases of human illness caused by the virus within this region. The notable clustering of the cases in two well-defined areas suggests the existence of specific environmental and social factors that increase the risk for WNV infection and/or illness in these locations. This investigation sought to create an empirically based model to account for these factors and to assess their importance in explaining the possible processes that may have led to this pattern.

Results

The cluster pattern of high incidence of cases was statistically significant. The risk factors that were found to be important included the presence of vegetation, age, income, and race of the human population, distance to a WNV positive dead bird specimen, age of housing, mosquito abatement and geological factors. The effect of different mosquito abatement efforts was particularly notable. About 53 percent of the variation of the location of WNV clusters was explained by these factors.

Conclusion

The models developed indicate that differential mosquito abatement efforts are especially important risk factors, even when controlling for key environmental factors. Human population characteristics play a role in risk that is measurable in this ecological study but would require further research to associate causality with risk. The analysis of spatial clusters of case incidence indicates that this approach provides more insight into the focal nature of differential risk factors that tend to be associated with WNV than an analysis of all individual cases.