The first human case of West Nile virus in Illinois has been confirmed by the U.S. Centers for Disease Control, according to the Illinois Department of Public Health.

The state agency announced Tuesday evening that a southern Illinois resident tested positive for the virus after being hospitalized. This is the earliest in the year that a human case of West Nile has been observed in Illinois since 2016, officials said.

While this is the first human case of the year, the West Nile virus had been confirmed in 19 counties so far, with the earliest detection in Rockford on May 9. The IDPH routinely tests batches of mosquitoes for West Nile and other mosquito-borne illnesses. Last year, the virus was found in 72 of Illinois’s 102 counties.

“The fact that we are seeing the first human case of West Nile virus so early in the season serves as a timely reminder — especially for seniors and those with weakened immune systems — to protect yourself from illnesses caused by mosquito bites,” IDPH Director Dr. Sameer Vohra said in a statement.

Last year, there were 69 cases of West Nile, 13 of which resulted in deaths. The majority of people infected with West Nile do not show symptoms, but for roughly 1 in 5 individuals, it can lead to severe illnesses. The risk is especially high for those older than 60 or with compromised immune systems.

The IDPH recommends that Illinois residents reduce their risk of contracting the disease by avoiding mosquito bites. This can be done through using EPA-registered mosquito repellants, especially those containing DEET, and by making sure that open doors and windows have screens. They also recommend dumping stagnant water that’s been standing for a week or more, as mosquitoes require standing water to reproduce. If you encounter standing water that you cannot pour out, it can be reported to 311.

West Nile virus is largely spread to humans through mosquito bites; it is rarely contagious between humans. It can also be found in birds and horses. West Nile is often transmitted from the Culex house mosquito, a medium-sized mosquito that is typically brown in color. Most mosquito bites occur early in the evening, but can occur any time of day.

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