RESEARCH our study and that of Gingritch and Casillas, only Oc. canadensis is relatively underrepresented by CDC light traps compared to Cx. pipiens, with a human landings to CDC light trap ratio of 1.31. However, this species is rarely infected with WNV and does not represent an important vector for transmitting WNV to humans (Table). One strength of our Risk measure is that it can be applied to other locations and at other scales simply by applying the risk equation to data from the desired scale and region if analyzed appropriately (26). In addition, the Risk equation can be used as a predictive index to forecast the relative number of future human WNV infections, which could be useful for short-term planning and resource allocation. The sum of the Risk equation over all (i = 1 to n) mosquito species multiplied by human population den- sity in the area considered should estimate the number of short-term future human WNV infections: Predicted human infections = (human density) × ∑ n i −=1 A × Fm × P × Cv We are currently testing the usefulness of this index in predicting the relative number of human WNV infections between locations and over the mosquito season. Acknowledgments We thank Barbara Willen, Kerri Harding, Michael Santoriello, and other Arthropod-Borne Disease Laboratory staff for trapping and identifying mosquitoes. We thank the local mos- quito districts of New York State for the collection of mosquitoes, the Arbovirus Laboratory staff for conducting WNV assays, and the New York State WNV surveillance team for coordinating sur- veillance efforts. This work was funded by National Institute of Allergy and Infectious Diseases (NIAID)–National Institutes of Health con- tract #NO1-AI-25490 and by core funding to the Consortium for Conservation Medicine at Wildlife Trust from the V. Kann Rasmussen Foundation. Funding for testing was partially provid- ed by the Emerging Laboratory Capacity grant from CDC, no. 15-0022-07. Blood meal analyses were funded by NIAID con- tract no. 14-0131-01. Dr. Kilpatrick is a senior research scientist at the Consortium for Conservation Medicine. His research interests include the ecology of zoonotic and wildlife diseases, communi- ty ecology, and conservation. References 1. Health Canada. West Nile virus monitor [surveillance data on the Internet]. [cited 2004 Dec 8]. Available from http://www.phac- aspc.gc.ca/wnv-vwn/mon_e.html 2. Centers for Disease Control and Prevention. West Nile virus [home- page on the Internet]. [cited 2004 Dec 6]. Available from http://www.cdc.gov/ncidod/dvbid/westnile/index.htm 3. Centers for Disease Control and Prevention. Epidemic/enzootic West Nile virus in the United States: guidelines for surveillance, preven- tion, and control [monograph on the Internet]. 3rd revision. 2003 [cited 2004 Dec 8]. Available from http://www.cdc.gov/ncidod/dvbid/ westnile/resources/wnv-guidelines-aug-2003.pdf 4. Turell MJ, Sardelis MR, O’Guinn ML, Dohm DJ. Japanese encephalitis and West Nile viruses. In: Mackenzie J, Barrett A, Deubel V, editors. Current topics in microbiology and immunology. Berlin: Springer-Verlag; 2002. p. 241–52. 5. Bernard KA, Maffei JG, Jones SA, Kauffman EB, Ebel GD, Dupuis AP, et al. West Nile virus infection in birds and mosquitoes, New York State, 2000. Emerg Infect Dis. 2001;7:679–85. 6. Duryea RD, Aedes trivittatus in New Jersey. Proceedings of the New Jersey Mosquito Control Association. 1990. p. 73–9. Available from http://www.rci.rutgers.edu/~insects/sp12.htm 7. Lombardi RW, Imber CF. The application of surveillance data to operational mosquito control. Proceedings of the New Jersey Mosquito Extermination Association. 1976;63:134–6. 8. Crabtree MB, Savage HM, Miller BR. Development of a species- diagnostic polymerase chain reaction assay for the identification of Culex vectors of St. Louis encephalitis virus based on interspecies sequence variation in ribosomal DNA spacers. Am J Trop Med Hyg. 1995;53:105–9. 9. Apperson CS, Harrison BA, Unnasch TR, Hassan HK, Irby WS, Savage HM, et al. Host-feeding habits of Culex and other mosquitoes (Diptera: Culicidae) in the borough of Queens in New York City, with characters and techniques for identification of Culex mosquitoes. J Med Entomol. 2002;39:777–85. 10. Apperson CS, Hassan HK, Harrison BA, Savage HM, Aspen SE, Farajollahi A, et al. Host feeding patterns of established and potential mosquito vectors of West Nile virus in the eastern United States. Vector Borne Zoonotic Dis. 2004;4:71–82. 11. Kauffman E, Jones S, Dupuis A II, Ngo K, Bernard K, Kramer LD. Virus detection protocols for West Nile virus in vertebrate and mos- quito specimens. J Clin Microbiol. 2003;41:3661–7. 12. Ngo KA, Kramer LD. Identification of mosquito bloodmeals using polymerase chain reaction (PCR) with order-specific primers. J Med Entomol. 2003;40:215–22. 13. Tempelis CH. Host-feeding patterns of mosquitoes, with a review of advances in analysis of blood meals by serology. J Med Entomol. 1974;11:635–53. 14. Spielman A. Structure and seasonality of nearctic Culex pipiens pop- ulations. Ann NY Acad Sci. 2001;951:220–34. 15. Fonseca DM, Keyghobadi N, Malcolm CA, Mehmet C, Schaffner F, Mogi M, et al. Emerging vectors in the Culex pipiens complex. Science. 2004;303:1535–8. 16. Turell MJ, O’Guinn ML, Dohm DJ, Jones JW. Vector competence of North American mosquitoes (Diptera: Culicidae) for West Nile virus. J Med Entomol. 2001;38:130–4. 17. Sardelis MR, Turell MJ, Dohm DJ, O’Guinn ML. Vector competence of selected North American Culex and Coquillettidia mosquitoes for West Nile virus. Emerg Infect Dis. 2001;7:1018–22. 18. Turell MJ, O’Guinn M, Oliver J. Potential for New York mosquitoes to transmit West Nile virus. Am J Trop Med Hyg. 2000;62:413–4. 19. Goddard LB, Roth AE, Reisen WK, Scott TW. Vector competence of California mosquitoes for West Nile virus. Emerg Infect Dis. 2002;8:1385–91. 20. Pratt HD, Moore CG. Mosquitoes of public health importance and their control. Atlanta: Centers for Disease Control and Prevention; 1993. 21. Rutledge CR, Day JF, Lord CC, Stark LM, Tabachnick WJ. West Nile virus infection rates in Culex nigripalpus (Diptera: culicidae) do not reflect transmission rates in Florida. J Med Entomol. 2003;40:253-8. 428 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 11, No. 3, March 2005