Jeena Galvin-Martin, who has visited Yosemite annually since she was a child and stayed in a Signature Cabin with her two young children in early August, said she's never been warned about hantavirus at the park.
"It's nature, I know, but I've never really heard of anything like this before," she said, adding that she's been nervously watching her 3-year-old and her 11-year-old for signs of the illness since she heard about the scare.
The virus takes one to six weeks to incubate, leaving people frightened and uncertain that they could come down with it long after leaving the park. Flulike symptoms -- chills, muscle aches, fevers -- initially appear, and the disease progresses rapidly. Within a day or two it can be very difficult to breathe. People who stayed at the campsite have been urged to visit their doctors at the onset of any symptoms.
This week, officials sent health advisory emails out to the 3,000 people who stayed in the 91 "Signature Cabins" from June 10 through Aug. 24. The Signature Cabins were built in 2009, but have a structural problem that allows mice to get in. The cabins have been vacated and are being cleaned and retrofitted to become "completely mouse-proof," Cobb said.
The park is also receiving 1,000 calls a day to its hantavirus hotline, which was set up Tuesday to field questions from worried campers, according to the Associated Press.
Valerna said he was so angry no one told him about the virus when he was a park guest that he called Yosemite on Tuesday and pretended he wanted to make a trip reservation just to see whether the park officials on the phone would warn him. They didn't, even when he asked whether anything dangerous was going on, he said.
"I said, 'Hey, listen, I just came from there. I know about the virus outbreak,'" Valerna said, prompting the official to tell him about the mice trappings and construction. "Somebody died in July. That's all I need to know."
But Schaffner said there are so many factors at play with hantavirus that it's impossible to prevent completely – even if the tent is reasonably clean.
In fact, hantavirus is not necessarily an outbreak as much as it's a collection of factors that resulted in a few human cases, he said. The number of mice and people in a given area as well as the drought and water availability indoors were all probably factors at play. He added that confined spaces offer more opportunity for an individual to inhale an "infectious dose" of the virus because it's more concentrated indoors than in the open air.
"I don't think there's anyone to blame," he said, adding that if park officials warned everyone and only four known cases occurred, they would be considered alarmist. "They're damned if they do, damned if they don't."