Report: Yosemite workers tested for Hantavirus

The testing is part of a pilot program for the park's 2,500 employees, to see how many were infected with the disease but aren't showing symptoms, reports KTVU-TV in Oakland, California.

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

People can get infected with hantavirus by inhaling it from rodent urine, feces or saliva. It can develop into Hantavirus Pulmonary Syndrome (HPS) and cause flu-like symptoms. The disease kills about 38 percent of people who become infected. Even healthy individuals are at risk for the pulmonary infection if exposed to the virus, according to the Centers for Disease Control and Prevention. Within four to 10 days of infection, people may experience coughing and shortness of breath that one HPS survivor described the feeling like a "tight band around my chest and a pillow over my face."

KTVU also reports the workers were given a questionnaire to fill out on their activities at work and home.

"We know that when people get sick from hantavirus and show symptoms that the mortality rate is very high. And they get very, very sick and many die," said Dr. Marty Fenstersheib, the Santa Clara County Public Health Officer. "So it would be really important to know, for any health official, to really understand is that just a small portion of the total number?'"

KTVU also reports the employees have been ordered not to discuss the testing.

It's not known when the tests will be completed or if they will be made public.

(Watch left for the CBS Evening News report on criticism over the park's response to the outbreak).