Two residents of a Virginia assisted living facility have died and 18 more have been hospitalized with respiratory symptoms in the past 11 days, prompting Fairfax County health officials to launch an outbreak investigation at the Springfield facility, officials said Thursday.

The Fairfax County Health Department announced the probe of Greenspring after 54 residents out of 263 were reported to be ill with symptoms ranging from coughs to pneumonia, department officials said in a statement.

The cause of death of the two residents was not immediately identified, the statement said, but tests are being conducted by the Virginia Department of Health and the Inova Health System.

The statement said the facility has cooperated with health officials and “appropriate measures have been taken to reduce the risk of infection and keep residents safe, including closing the facility to new admissions, canceling group activities, keeping ill residents in their rooms, and increasing cleaning.”

A call to Greenspring was not returned Thursday, and the facility’s leadership could not be reached.