The Maryland Department of Health and Mental Hygiene announced Thursday that a Baltimore area adult is the state’s first confirmed case of West Nile virus infection in 2011.

West Nile virus is endemic in Maryland, and health officials typically see cases every year.

On July 26, the D.C. Department of Health announced it had positively identified West Nile in several mosquito samples in the Woodley Park, Adams Morgan and North Cleveland Park neighborhoods of the District. The virus has also been reported in Fairfax County, and Maryland health officials said three pools of mosquitoes collected in Montgomery County by the U.S. Department of Defense tested positive for West Nile virus infection.

The disease, an infection of birds which is picked up by mosquitoes and can spread to humans, has plagued the area since 1999, when it was identified near Baltimore. At its peak in 2002, 10 people in the District, Maryland and Virginia died from the infection.

Nationwide since 1999, 1,220 people have died from the virus; 25 were from the District, Maryland or Virginia. The virus generally takes a bigger toll on birds than on humans, however. Several common North American bird species have suffered drastic population declines since its arrival, leaving rural and suburban areas quieter than they used to be and causing ecological stresses on a variety of animals and plants, a 2007 study found.

Senior citizens or those who have compromised immune systems are encouraged to stay indoors during periods when mosquitoes are active. Everyone else should use mosquito repellants and dispose of any outdoor containers where water could collect, which makes an ideal spot for insect larvae, health officials said.