(CBS) — With the wettest May on record in Chicago, concerns about a bumper crop of mosquitoes–and potential for West Nile virus–have public health officials on alert.

The Chicago Department of Public Health began its annual mosquito control activities on May 15. By mid-June, the city will have treated 80,000 catch basins in Chicago with larvicide, which kills immature mosquitoes. Extended-release larvicide briquettes will provide control all summer.

Starting on Monday, the health department will set a total of 83 traps across the city, and samples will be tested weekly for West Nile Virus.

The suburbs are also taking precautions.

In recent tests, a total of five mosquitoes tested positive for West Nile, according to North Shore Mosquito Abatement District. The risk to humans right now is low, according to the district.

The positive tests were recorded on May 20 and May 22 in Evanston, Glencoe Glenview, Northbrook and Winnetka.

The public can take steps to reduce the West Nile risk:

Use insect repellent;

Wear loose fitting clothing;

Avoid peak mosquito feeding times during the hours around dawn and dusk.

Eliminate any items that can hold water, particularly smaller items that may be easily overlooked.

West Nile virus is the leading cause of mosquito-borne disease in the continental United States, according to the CDC.

About 1 in 5 people who are infected develop a fever and other symptoms.

About 1 out of 150 infected people develop a serious, sometimes fatal, illness like encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord). The elderly are most at-risk.

No vaccine or specific antiviral treatments for West Nile virus infection are available. Over-the-counter pain relievers can be used to reduce fever.