In someways this is totally scary. However, it doesn't really surprise me that Yosemite keeps getting these disease outbreaks.
Last year Yosemite saw 6 million visitors (The populations of LA and San Diego combined). It is the second busiest NP (after Yellowstone, I believe). It is also a very small place and as such a geographic bottleneck.
There was also a Hanta outbreak a couple of years back in Yosemite.

Looking at this map there is the greatest concentration in the Four Corners area with assorted out breaks around the West. Hanta is also concentrated in the FC region.
My thought is that both the FC areas and Yosemite are highly visited natural recreation areas, and often people will take long vacations visiting multiple wilderness areas. With tourists traveling from specific natural area to specific natural area it doesn't surprise me that these diseases show up in these concentrated areas.
Still, if you use a tent, keep a clean site, and don't touch the rodents you shouldn't have too much trouble.
I was just in Yosemite this week, even on a Monday the people speaking various languages rivaled the English speaking visitors in numbers. In that regard it was pretty cool to see that many people of such diversity enjoying the Valley, however there is a dark side to the park crowds...
I also witnessed a couple of people (who were either oblivious, stupid, or couldn't read English) feeding squirrels sitting beneath a big full-color sign pleading visitors not to feed the animals (with a picture of the same species of ground squirrel they were feeding).
Natural selection?
BTW Last I saw on FB, Gary was visiting Savannah, fit as a fiddle
