May 20, 2022: the Centers for Disease Control and Prevention listed six Connecticut Counties in the High/Orange category as part of its COVID-19 Community Levels Map. Only Fairfield and Tolland Counties are listed in the Medium/Yellow category. Residents in these counties should wear a mask indoors in public; stay up to date with COVID-19 vaccines and get tested if they have symptoms. Additional precautions may be needed for residents who are at high risk for severe illness. Visit the CDC COVID-19 Community Levels Map for updates.

Saint Louis Encephalitis

Culex pipiens


Saint (St.) Louis Encephalitis virus (SLEV) is spread to people through the bite of infected mosquitoes. This virus is found in mosquitoes from Canada to Argentina although most human cases of disease have occurred in the United States. No cases have been reported from Connecticut. There is no vaccine to prevent or medicine to treat SLEV virus infection. The best way to prevent getting sick from SLEV is to prevent mosquito bites.


About St. Louis Encephalitis


Where in the United States Has SLEV Been Found?

ArboNET National Data


Information for Clinicians


Clinical Guidance

National Surveillance Case Definition


Connecticut Provider Reporting Information 

Reportable Disease Confidential Case Report form, PD-23

Connecticut Laboratory Reporting Information

Reportable Laboratory Findings form, OL-15C


SLEV testing at the State Public Health Laboratory

State Public Health Laboratory Contacts – for additional information


Connecticut St. Louis Encephalitis Surveillance

In 2000, encephalitis was added to the state-wide reportable disease list, which included Saint Louis encephalitis (SLE). There have been no reported cases of SLE to the Connecticut Department of Public Health.

Connecticut Annual Infectious Diseases Statistics

Additional Resources

Connecticut Mosquito Management Program

Workplace Safety - Mosquito-Borne Diseases   NIOSH




This page last updated 8/11/2020.