Test results for a dead bird found in DeKalb County came back negative for West Nile virus on Monday, but local officials said it’s only a matter of time until a bird tests positive.

The Illinois Department of Public Health reports 27 birds in 17 Illinois counties have been confirmed to have the virus since May 1.

“While some types of mosquitoes transmit West Nile and other viruses, not all do,” said Karen Grush, public health administrator at the DeKalb County Health Department.

“Fortunately, the increase in mosquito population is primarily in the type of mosquitoes that do not transmit West Nile infection,” Grush said.

The recent rains have caused an increase in the number of mosquitoes in the area. Nuisance or floodwater mosquitoes are present after heavy rainfall because their eggs must become wet to develop, according to the DeKalb County Health Department. They bite primarily in the day and aren’t typically capable of transmitting disease.

“While floodwater mosquitoes are not a cause for concern, we will soon see an increase in the vector mosquitoes, including those that can carry West Nile virus,” said Bob Drake, director of the environmental health division with the county health department.

Vector mosquitoes usually transmit viruses they get from feeding on infected birds0. They bite primarily in early morning or around dusk.

According to the DeKalb County Health Department, just one in 100,000 people becomes infected, and most mosquitoes don’t carry the virus. Persons 50 years of age and older are at highest risk of serious illness related to the mosquito-borne disease.