West Nile Virus: Data

The first cases of West Nile virus (WNV) in humans in Wisconsin were reported in 2002.

In 2020, Wisconsin had five confirmed and probable cases of West Nile virus.

From 2016 through 2020, an average of 21 cases of West Nile virus have been reported each year. West Nile virus is preventable.

You can see the statewide data for West Nile virus in the table.

For information on national data, visit the Centers for Disease Control and Prevention (CDC) Statistics and Epidemiology page for West Nile virus.

Case numbers are updated routinely during mosquito season.

2021 Wisconsin WNV Case Data

Updated January 13, 2022

Human confirmed 5
Human probable* 1
Deaths** 0
Hospitalizations 5
Equine (horse) 1
Mosquito pools (no mosquito testing occurred in 2021) 0
Counties reporting WNV activity 7

* Probable cases have presumptive positive laboratory results without  confirmatory testing at CDC.
** The deaths are included among the confirmed and probable cases.

West Nile virus activity by county, Wisconsin 2021

West Nile Virus Data

West Nile Virus Cases in Wisconsin (2002-2020)

Graph showing West Nile Virus cases in Wisconsin

Cases Reported by Month and Age

Month of Illness Onset

West Nile virus cases by month

Age Group

West Nile virus cases by age group

Questions about illnesses spread by mosquitoes? Contact us!
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Last Revised: June 15, 2022