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About West Nile

Cases of West Nile virus (WNV) have been reported in states across the continental United States. WNV activity typically occurs during the summer months and into the fall. The annual number of reported WNV disease cases can fluctuate widely, as a result of periodic epidemics. All residents of and visitors to areas where WNV activity has been identified are at risk of WNV infection, particularly people who engage in outdoor work and recreational activities.

West Nile virus disease is a nationally notifiable condition. Cases are reported to CDC by state and local health departments using standard case definitions. Arboviral surveillance data are reported to CDC through ArboNET. In addition to human disease, ArboNET maintains data on arboviral infections among presumptive viremic blood donors, veterinary disease cases, mosquitoes, dead birds, and sentinel animals.