Two people have died and 18 others have been hospitalized after a "respiratory outbreak" at a Virginia retirement community, according to officials.

The Fairfax County Department of Health said that 54 individuals had become ill with "respiratory symptoms ranging from upper respiratory symptoms (cough) to pneumonia" in the last 11 days at Greenspring Retirement Community in Springfield.

In a letter Wednesday to residents obtained by ABC News affiliate WJLA-TV in Washington D.C., Greenspring described symptoms as "fever, cough, body aches, wheezing, hoarseness and general weakness."

Benjamin Schwartz, a health department director, told ABC News on Thursday that the outbreak had been reported in the assisted-living and skilled-nursing sections. He said the outbreak began with the first case on June 30.

The specific cause of the outbreak had not yet been identified but additional tests of samples were being done, according to Schwartz.

The assisted-living and skilled-nursing facility in Greenspring is home to 263 residents, Schwartz said. He said the two patients who died in the outbreak had been hospitalized with pneumonia but were "older individuals with complex medical problems."

"One of the things about skilled nursing facilities and assisted living facilities is [that] when you have a lot of people in close proximity, who have underlying medical conditions, there is an increased risk for outbreaks," he said. "Seeing a respiratory outbreak in a long-term care facility is not odd. ... One thing that's different about this outbreak is just that it's occurring in the summer when, usually, we don't have a lot of respiratory disease."

Of those initially hospitalized, seven have returned to the retirement home, said Courtney Benoff, regional communications manager for Erikson Living, which owns the retirement home.

The health department said that although there had been no new hospitalizations in the "past couple of days," residents were still getting sick in the outbreak.

In a statement, Greenspring said that its "highest priority is the welfare of those who live and work on campus."

"In keeping with this commitment the community has acted with an abundance of caution, and in partnership with the Fairfax County Department of Health, has taken all necessary measures to fully implement proven infection prevention and control strategies. We remain vigilant in our response and will continue to provide frequent and transparent updates to residents, staff and family members," the retirement home said in a statement.

The Fairfax County Health Department said it is investigating the incident.

The department said that appropriate measures had been taken to reduce the risk of infection and keep residents safe, including closing the facility to new admissions, cancelling group activities, keeping ill residents in their rooms and increasing cleaning.

Residents experiencing any of those symptoms were urged to call the community's medical center.