About 100 Yosemite National Park employees participated in voluntary hantavirus testing, survey and questionnaire Sept. 26 as part of a pilot program the park hopes to launch by next month for more park employees, said park spokesman Tom Medema.

Nine case of hantavirus, a rare disease contracted from rodents, were traced to Yosemite since mid-June, killing three visitors. The park continues to investigate the outbreak.

"California Department of Public Health wants to know if incidents that led to exposure in Yosemite are the same or different than the rest of the U.S. population," Medema said.

The Sept. 26 blood tests searched for specific antibodies, and could determine if a person has ever been exposed to hantavirus, Medema said.