The New York State Department of Health says evidence of West Nile virus was found in two different mosquito pools in Oswego County.
Both pools previously tested positive for the virus this summer and the latest collections were taken before the county sprayed the area on September 11.
Health officials are reminding people that aerial spraying does not kill all infected mosquitoes. Using insect repellant, limiting activities when mosquitoes are active, wearing long clothing and eliminating all standing water can reduce the risk of exposure.
At the end of August, health officials said there have been 13 human cases of West Nile virus infection in New York so far this year, including the deaths of two older people. One was in Onondaga County.
A national West Nile outbreak this year involves many cases in Texas.