The Illinois Department of Public Health (IDPH) has announced that the first mosquito pool of the year to test positive for West Nile virus (WNV) was collected on May 9 in Rockford by the Winnebago County Health Department. The specimen tested positive for WNV on May 12.

Last year, 72 counties in Illinois reported positive tests for WNV in mosquitos, birds, horses, or humans. According to IDPH data, there were 69 confirmed human cases of WNV and 13 human deaths, marking the highest number since 17 deaths were recorded in 2018.

The IDPH maintains a robust surveillance system to monitor WNV in the environment through laboratory testing of mosquito batches and sick horses, as well as among Illinois residents by investigating and monitoring human infections.

West Nile virus is transmitted through the bite of a Culex mosquito, commonly known as a house mosquito, that has fed on an infected bird. Common symptoms include fever, nausea, headache, and muscle aches, which may last from a few days to a few weeks. Most people infected with West Nile virus will not show any symptoms; however, in rare cases, severe illness, including meningitis, encephalitis, or even death, can occur. People older than 60 and individuals with weakened immune systems are at higher risk for severe illness from West Nile virus.