West Nile Virus: Data
The first cases of West Nile virus in humans in Wisconsin were reported in 2002. On average, 18 cases of West Nile virus are reported each year in the state.
In 2023, Wisconsin had 25 confirmed and probable cases of West Nile virus.
West Nile virus is preventable.
You can see this year's statewide data for West Nile virus in the table and the map on this page. Case numbers are updated routinely during mosquito season.
Summary data for all other years can be found at the bottom of this page.
For more detailed data by county, visit the Wisconsin Environmental Public Health Tracking: West Nile Virus Data.
For information on national data, visit the CDC (Centers for Disease Control and Prevention) Data and Maps page for West Nile virus.
| Type | Number of cases |
|---|---|
| Human confirmed | 18 |
| Human probable* | 14 |
| Deaths** | 3 |
| Hospitalizations** | 23 |
| Presumptive viremic donors‡ | 9 |
| Mosquito pools | 26 |
| Horses | 9 |
| Birds | 3 |
| Counties reporting West Nile virus activity | 28 |
*Probable cases have presumptive positive laboratory results without confirmatory testing at CDC.
**Deaths and hospitalizations are included among the confirmed and probable cases.
‡Presumptive viremic donors are healthy blood donors whose blood tested positive for West Nile virus.
Historical West Nile virus data
Month of illness onset
Age group
Questions about illnesses spread by mosquitoes? Contact us!
Phone: 608-267-9003 | Fax: 608-261-4976