Yosemite National Park officials are stepping up their efforts to alert past visitors to its Curry Village that they may have been exposed to hantavirus. Some 2,900 letters and emails have now been sent to people who bunked in a "signature tent cabin" between June 10 and Aug. 24, reports the LA Times. Two campers have died of the rodent-spread illness, and authorities have confirmed one other case and identified a likely one. Park officials are now working with the CDC to spread the word nationwide. "The notification is our No. 1 priority," says an epidemiologist. "We want to come up with other strategies to make sure that people hear about this."