I haven't been to Yosemite in years (three years to be exact) so I don't think I have to worry about this hantavirus outbreak, which has led to the deaths of about three people. It seems to be focused more on people who stayed in the cabins since they found rodent feces in some of the cabins that could have caused the virus.
Don't let this scare you away from a visit to this park, known for its half dome mountain, huge water falls, and larger than life trees. I'm sure the park is spic n' span now.

But if you did go recently and stayed in a cabin - I'd go to your doctor just in case.