YOSEMITE NATIONAL PARK  (AP) — California public health officials want to survey workers at Yosemite National Park to determine whether they were exposed to a deadly mouse-borne virus, a park spokesman said Thursday.

The California Department of Public Health recently proposed to take a voluntary survey of workers to contribute to the park's understanding of the rare virus and the recent disease cluster, Yosemite National Park spokesman John Quinley said.

Quinley added that state and federal public health officials are still designing and reviewing the proposed survey and will notify employees if it goes forward.

The Mariposa Gazette reported Thursday that three workers in Yosemite National Park experienced flu-like symptoms and got tested for hantavirus.

Mariposa County Health Officer Charles Mosher told the Mariposa County Board of Supervisors at a meeting Tuesday that while initial tests came up positive, a set of second set of tests showed the workers were not exposed to the strain that causes hantavirus pulmonary syndrome, the paper reported.

Quinley said there have been no confirmed or suspected cases among employees of the National Park Service or the park's concessionaire, DNC Parks and Resort.

Nine people who spent time at the park this summer have been infected with the rodent-borne virus, the majority after staying at the "Signature" cabins in Curry Village. Three of them have died.