CHAMPAIGN – If you've got outdoor plans for Labor Day weekend, don't forget the insect repellent.

West Nile virus is picking up, and a hot September could boost the risk for more human cases, state health officials say.

Champaign-Urbana Public Health District Administrator Julie Pryde said there have been many mosquito batches and dead birds in Champaign County that have tested positive for West Nile virus this summer.

"People need to keep wearing their bug spray," she said. "There seems to be this mental thing out there that once the Fourth of July is over, they don't have to worry about mosquitoes any more."

Labor Day weekend is a prime time for West Nile infection because so many people will be outdoors, Pryde added.

The first human West Nile case in the state this season – a woman in her 50s – was reported Tuesday in DuPage County.

The woman began experiencing the symptoms, which typically include fever, headache and body ache, in early August, according to the Illinois Department of Public Health.

To date, virus-positive mosquito and bird batches have been found in 25 Illinois counties, but the Illinois Natural History Survey is now reporting a big upswing in positive West Nile virus mosquito samples.

In Champaign County, virus-positive birds or mosquitoes have been found in Champaign, Urbana, western Champaign County and Tolono, said Jim Roberts, C-U Public Health District environmental health director.

Last year, West Nile Virus was in about one-third of the state's counties, and there wound up being five human cases, according to the Illinois Department of Public Health.

What are your chances of getting West Nile virus? About two out of 10 people bitten by an infected mosquito will become ill, and people over 50 are most at risk for serious illness. People usually get mild flu-like symptoms, but some serious cases can result in encephalitis or meningitis. The virus can also be fatal.

Pryde said there's no way to tell the difference between West Nile virus and the flu strain that's also now circulating in the area.

"It can only be confirmed by testing, and the only way you're diagnosed is if you're hospitalized," she said.

The best defense against West Nile virus remains preventing mosquito bites: Wear protective clothing, use insect repellent, eliminate standing water around the home, make sure window and door screens aren't loose and avoid being outdoors when mosquitoes are most active – from dawn to dusk, health experts advise.