An adult East Lyme resident contracted the deadly mosquito-borne virus that causes eastern equine encephalitis last month and remains hospitalized, state health officials announced Monday afternoon.

The resident, whose identity and gender were withheld, became ill with encephalitis during the last week of August, the state Department of Public Health announced. Tests completed Monday at the Centers for Disease Control and Prevention laboratory in Fort Collins, Colo., confirmed the presence of the antibodies that fight the virus that causes EEE.

“EEE is a rare but serious and potentially fatal disease that can affect people of all ages,” DPH Commissioner Renée Coleman Mitchell said in a statement. “Using insect repellent, covering bare skin and avoiding being outdoors from dusk to dawn are effective ways to help keep you from being bitten by mosquitoes.”

The virus has been identified in mosquitoes trapped in 12 towns and in horses in two other towns.

Towns where mosquitoes have tested positive include Chester, Haddam, Hampton, Groton, Killingworth, Ledyard, Madison, North Stonington, Plainfield, Shelton, Stonington and Voluntown. Horses have tested positive in Colchester and Columbia.

The virus also has been detected in a flock of wild pheasants.

The East Lyme resident is the second confirmed human case of EEE ever reported in Connecticut. The first case, in the fall of 2013, resulted in the death of a Killingly resident.

In the earlier case, the patient, after suffering three days of fever and severe headaches, was hospitalized with a preliminary diagnosis of meningitis. The patient died five days after being admitted to the hospital, according to a DPH publication.

The patient, an otherwise healthy person, participated in recreational activities in locations that may have harbored EEE-infected mosquitoes.

School and recreation officials in the southeastern Connecticut towns where infected mosquitoes have been trapped this summer have taken steps to limit outdoor activity during dusk and dawn.

In a letter to parents Monday, Jeffrey Newton, the East Lyme superintendent of schools, announced the schools’ athletic department was working to adjust schedules of practices and games to protect students.

“Our goal is to move athletic events to earlier in the afternoon so that all students are off the field by 5:30 p.m.,” Newton wrote.

Officials in Ledyard, Groton and Stonington have announced similar action.

The threat posed by infected mosquitoes will continue until the first hard frost, which could come as late as mid-October.

The DPH advises against unnecessary trips into mosquito breeding grounds and marshes as the mosquitoes that transmit EEE virus are associated with freshwater swamps and are most active at dusk and dawn. Overnight camping or other substantial outdoor exposure in freshwater swamps should be avoided.

Although infected mosquitoes continue to be detected in southeastern Connecticut, their numbers are declining, and the state is not experiencing the excessively high levels of activity seen in Massachusetts, the DPH said.

Connecticut officials currently have no plans to implement widespread aerial pesticide spraying in the state.

Massachusetts has had eight human EEE cases, one of which, a Fairhaven woman, proved fatal. Rhode Island has had one human case, in West Warwick, which was fatal.

b.hallenbeck@theday.com