La Crosse Encephalitis Statistics

The first case of La Crosse encephalitis ever reported was in the early 1960’s in a Houston County, MN resident. The child died in a La Crosse, Wisconsin hospital, and the disease was subsequently named after this city. The disease, which primarily affects children, is spread through the bite of infected Aedes triseriatus (Eastern Tree Hole) mosquitoes. Exposure to infected mosquitoes usually occurs in wooded or shaded areas, especially where water-holding containers (such as buckets, cans, or tires) provide good breeding habitat for the mosquito. 

Similar to other arboviruses, most La Crosse encephalitis cases occur later in the summer (July through September) when infected mosquito populations are at their highest level. La Crosse encephalitis is found in southeastern Minnesota, especially in counties along the Mississippi River. Since 1985, 148 cases have been reported from 24 Minnesota counties, primarily in the southeastern part of the state.

In 2022, three cases of La Crosse encephalitis were reported in Minnesota. 

• Cases were aged 4 and 6 years, and all but one of the cases were male
• All 3 cases presented with neuroinvasive disease, including meningitis and encephalitis, and were all residents of counties in southeastern Minnesota
   

Maps and graphs:

• Reported Cases of La Crosse Encephalitis by Year, Minnesota, 1985-2022 (PDF)
  Graph of reported cases of La Crosse encephalitis in Minnesota by year.
• Reported Cases of La Crosse Encephalitis by County of Residence, Minnesota, 1985-2022 (PDF)
  Map of reported cases of La Crosse encephalitis by county of residence.

Annual Summary Statistics

• Endemic Mosquitoborne & Tickborne Arboviral Diseases: Annual Summary of Reportable Diseases
  The Minnesota Department of Health collects information on infectious diseases for the purposes of determining disease impact, assessing trends in disease occurrence, characterizing affected populations, prioritizing control efforts, and evaluating prevention strategies, and reports statistics annually. Note: There are no listings for years in which there were no cases reported. The annual summary archives available on the web go back to 1997.

National statistics

• CDC: La Crosse Encephalitis Data and Maps 
  Maps, charts, tables, and reports from the CDC.