West Nile Virus–infected Mosquitoes, Louisiana, 2002

Human cases of West Nile virus (WNV) disease appeared in St. Tammany and Tangipahoa Parishes in southeastern Louisiana in June 2002. Cases peaked during July, then rapidly declined. We conducted mosquito collections from August 3 to August 15 at residences of patients with confirmed and suspected WNV disease to estimate species composition, relative abundance, and WNV infection rates. A total of 31,215 mosquitoes representing 25 species were collected by using primarily gravid traps and CO2-baited light traps. Mosquitoes containing WNV RNA were obtained from 5 of 11 confirmed case sites and from 1 of 3 sites with non-WNV disease. WNV RNA was detected in 9 mosquito pools, including 7 Culex quinquefasciatus, 1 Cx. salinarius, and 1 Coquillettidia perturbans. Mosquito infection rates among sites ranged from 0.8/1,000 to 10.9/1,000. Results suggest that Cx. quinquefasciatus was the primary epizootic/epidemic vector, with other species possibly playing a secondary role.