About the WNV data

This page provides general information about West Nile Virus (WNV) and measures developed by the Minnesota Environmental Public Health Tracking (MN Tracking) Program. For more information about these data, contact MN Public Health Data Access.


For confirmed human WNV cases in Minnesota:

  • The numbers of WNV by year, month, sex, or age group in Minnesota.
  • If a segment of a population is at higher risk for WNV.
  • If a measure is going up or down over time.
  • Provide information to the public about WNV in Minnesota.
  • State and local partners can use these data for program planning and evaluation.
  • Inform prevention guidelines for targeted public awareness and prevention campaigns during peak mosquito season.
  • MDH Vectorborne Disease Unit and the MN MDH Climate and Health Program can use these data to inform their programs. 
  • The total burden of WNV in a population, since not all WNV cases are diagnosed or reported.
  • Where the person was when they were exposed to the infected mosquito.
  • The number or rate of occupationally-acquired WNV in Minnesota.
  • How much or if climate change has influenced WNV case numbers.
  • WNV is a notifiable condition, so data is collected by the MDH Vectorborne Diseases Unit under Minnesota statute 4605.7040 B. 


  • The number indicates the total number of confirmed human cases of WNV.


  • The map of WNV occurrence is based on the average incidence (cases/100,000 population) of WNV cases in Minnesota from 2002-2016. Annual incidence rates were calculated for each year and then averaged for the entire time period of 2002-2016. Cases are categorized by patient's county of residence, which may not represent exposure location.
  • Cases are Minnesota residents diagnosed with WNV reported to the Minnesota Department of Health by health care providers and diagnostic laboratories.
  • WNV is a nationally notifiable disease with a standard case definition based on clinically compatible illness and laboratory confirmation. 
  • Minnesotans need to see a health care provider and be diagnosed with WNV to be considered a case; those who do not seek medical care will not be included in the case count.
  • Most people infected with West Nile virus will be either asymptomatic or experience a flu-like illness. These cases will likely not seek care and not be included in the total case count.
  • Underreporting of WNV due to incomplete diagnostic testing is a significant concern for data quality. 
  • The rates are not age-adjusted. It is not appropriate to compare groups, such as age groups and counties, due to this limitation.