West Nile Virus: Data

The first case of West Nile virus in humans in Wisconsin was reported in 2002. In 2018, Wisconsin had 33 probable and confirmed cases of West Nile virus. Since 2002, on average, 19 cases of West Nile virus are reported each year. West Nile virus is preventable.

You can see the statewide data for West Nile virus in the table below. 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 weekly during mosquito season.

2019 Wisconsin Summary Data
Positive WNV Cases - Updated November 20, 2019

Human confirmed 2
Human probable* 0
Deaths** 0
Hospitalizations 0
Avian (bird) 2
Equine (horse) 0
Mosquito pools 45
Counties reporting WNV activity 5

* 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 2019

West Nile Virus Data

West Nile Virus Cases in Wisconsin (2002-2018)

West Nile Virus Cases in Wisconsin, 2002-2018.

Cases Reported by Month and Age

Month of Illness Onset

Average West Nile cases by month, 2014-2018.

Age Group

Average West Nile cases by age group, 2014-2018.

Questions about illnesses spread by mosquitoes? Contact us!
Phone: 608-267-9003 | Fax: 608-261-4976

Last Revised: November 20, 2019