NEW HAVEN — The state Department of Public Health on Friday reported the second case of West Nile virus in Connecticut this year.

A New Haven County resident in his 30s was hospitalized and diagnosed with the virus in early September, DPH officials said.

He remains in the hospital, officials said, although his condition is improving.

Scientists warned residents to remain cautious about exposing themselves to mosquitoes, which carry the disease, even as the weather cools.

"Residents should not be fooled by the cooler temperatures this weekend," DPH Commissioner Manisha Juthani said. "It is still important to take precautions to avoid mosquito bites. Using insect repellent, covering bare skin, and avoiding being outdoors during the hours of dusk and dawn are effective ways to help keep you from being bitten by mosquitoes."

The first West Nile case of the year was diagnosed in August, officials said.

As of Friday, the Connecticut Agricultural Experiment Station had detected mosquitoes carrying the virus in 24 municipalities across the state.

The communities where the virus has been detected include Branford, Bridgeport, Cornwall, Darien, Fairfield, Greenwich, Hartford, Ledyard, Meriden, Milford, New Canaan, New Haven, Newington, Norwalk, Stamford, Stratford, Wallingford, Waterbury, Waterford, West Haven, Westport, Wethersfield, Wilton and Woodstock, officials said.

"Mosquitoes are still active and West Nile virus continues to circulate in Connecticut. We anticipate continued risk for human infection until the first hard frost in October," said Philip Armstrong, medical entomologist at the Connecticut Agricultural Experiment Station.

West Nile virus has been detected in the state since 1999. It is the most prevalent mosquito-borne disease in the United States, according to the Department of Public Health.

Most people infected with the virus — about 8 out of 10 — never develop symptoms. About 1 in 5 people infected develop West Nile fever. Only about 1 in every 150 infected people develop a serious illness affecting the central nervous system, and about 1 in 10 of these severe illness cases can be fatal. People over the age of 60 are at the highest risk of serious illness, DPH said.