Toronto Public Health is reporting the first confirmed human case of West Nile virus in the city this year.

The agency says the infected person is an adult and that the case was confirmed through laboratory testing. West Nile virus is transmitted to people through the bite of an infected mosquito.

Dr. Lisa Berger, an associate medical officer of health, said in an interview on Tuesday that the person was bitten by a mosquito in Toronto but the agency is not releasing any other details about the person.

"Typically, the first positive case tells us that West Nile virus is circulating in the city," Berger said. 

"It tells us that it's here in Toronto. That's why we ask people living in the city to make sure they take the preventative measures that they can to reduce the chances of them being bitten by a mosquito. Anywhere in Toronto, a person could be at risk."

Berger said the number of cases, along with the date of the first confirmed human case, varies from year to year. Typically, West Nile virus infections tend to occur in the summer months, between July and September, with the peak usually in August or September.

She added that public health officials are not sure yet how many cases to expect this year.

"We don't have a strong indication yet of the severity of the season. It depends also on weather conditions going forward. That's just difficult to predict."

Toronto had 39 confirmed cases last year

Last year, there were 39 confirmed human cases of West Nile virus in Toronto. Public Health says the first human case of virus in the city last year was reported on July 27.

The risk of acquiring a West Nile virus infection in Toronto is low, Berger added.

"There aren't a lot of mosquitoes that are infected here right now," she said.

Symptoms of the virus usually develop two to 14 days after a person is bitten by an infected mosquito. They can include fever, headache, nausea, vomiting, body aches, skin rash and swollen lymph glands. About 80 per cent of people infected with West Nile virus show no symptoms.

Older people who have compromised immune symptoms face a higher risk of severe illness.

Toronto Public Health recommends that residents do the following to avoid becoming infected with West Nile virus

• Wear light-coloured clothing, long pants and long-sleeved shirts when outdoors.
• Apply insect repellent containing DEET or icaridin. 
• Take extra care by using repellent and covering up during peak mosquito-biting hours when mosquitoes bite, which is dusk and dawn.
• Ensure your home has tight-fitting screens on windows and doors.
• Remove standing water from your property, where mosquitoes can breed. That includes any water that collects such items as buckets, planters, toys and waste containers.

West Nile virus was first identified in North America in 1999. The first confirmed human case of the illness in Canada appeared in Ontario in 2002.