Fairfax County health officials said they don't yet have a cause of the respiratory illness that sicked more than 60 residents at a Northern Virginia senior living community.

The outbreak at Greenspring Retirement Community in Springfield began June 30. Sick residents had symptoms such as coughs, fevers and pneumonia.

Three people have also died, but Dr. Benjamin Schwartz of the Fairfax County Health Department said Wednesday afternoon that those who died were "older" and had complex health problems. Officials don't yet know the extent to which the respiratory illness contributed to their deaths, he said.

The community has implemented infection-prevention measures including cancelling group activities, increasing cleaning, isolating infected patients in their rooms and restricting visitors, Schwartz said.

"The facility has done an excellent job implementing those infection-prevention measures," he said.

The outbreak was reported in the assisted living and skilled nursing areas of the community, where about 263 people live. The outbreak has now affected 63 of those residents. At least 20 were taken to a hospital.

There were no problems reported among the residents of the independent living portion of the community.

Health officials said last week what was striking about the outbreak was the number of residents impacted and the time of year — summer instead of winter, when flu and respiratory illness usually spread.

Greenspring is working with the Fairfax County Health Department to try to stem the spread of the illness.

Greenspring issued a statement last week that read, in part, "Greenspring's highest priority is the welfare of those who live and work on campus … In partnership with the Fairfax County Department of Health, (Greenspring) has taken all necessary measures to fully implement proven infection prevention and control strategies."

The health department has sent several samples from infected patients to the Centers for Disease Control and Prevention for testing, but no cause for the outbreak has been identified, Schwartz said.

The health department is continuing to work with the facility on the investigation, he said. Testing for Legionnaires disease was negative, he said.

Schwartz said there were also reports of a respiratory illness outbreak at an assisted living facility several miles away in Burke, Virginia. About 25 people were ill there, including two with pneumonia; there have been no deaths. He said there is "no evidence of any connection whatsoever" between the two outbreaks.