About West Nile

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

West Nile 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.