Rather, people should wear gloves and use bleach where they see mouse droppings. They should let the bleach sit for 15 minutes before using a mop or sponge to clean up.

Opening shuttered areas to air and sunlight also is suggested.

The two recent hantavirus cases bring the 2012 total in California to four. About one-third of the 60 cases reported in the state since 1993 have been fatal, the department said. Yosemite National Park saw one hantavirus case each in 2000 and 2010.

There is no specific treatment for hantavirus infection, according to the CDC, but the earlier the patient is brought to intensive care, the better.

Diagnosis is difficult, because early symptoms of fever, muscle aches and fatigue often are confused with the flu.

"However, if the individual is experiencing fever and fatigue, and has a history of potential rural rodent exposure, together with shortness of breath, (that) would be strongly suggestive of HPS," the CDC says.