Mosquitoes testing positive for the virus were found at Country Commons Park at North and Charles avenues, Hobson Grove Park on Olesen Lane near Hobson Mill Drive and Knoch Knolls Park on Knoch Knolls Road.

City officials earlier this month discovered infected mosquitoes at Springhill Park, along Plank Road near Milton Drive. It's one of 16 city trapping sites.

The potentially fatal virus, which has been in the Midwest for four years, is spread through the bite of an infected mosquito. No human cases or deaths have been reported in the state this year.

Increased Surveillance

More than 140 mosquito samples have tested positive for the virus in the state as of Wednesday, according to the Illinois Department of Public Health.

Naperville Public Works Director Dave Van Vooren said surveillance efforts for breeding sites will be increased within a mile radius of the three trapping sites and additional monitoring traps will be set up. Mosquitoes found in the traps will be re-tested for the virus twice a week.

"We encourage Naperville residents to continue taking the same precautions that have been in place now for the past four years," Van Vooren said.

Severe Complications Rare

Most people who are bitten don't get sick, though some may have flu-like symptoms. In rare cases, the virus can cause encephalitis or meningitis.

To reduce the risk of mosquito bites, people should use repellant outside, eliminate standing water around their homes, repair any tears in screens and keep roof gutters clear of debris.