"We know they had rodent exposure," because that's how the virus is spread, she said."We just don't know where. We're still investigating."
Summer is peak season for hantavirus, which is carried predominantly by deer mice in North America. People are usually exposed by breathing contaminated dust after disturbing or cleaning rodent dropping or nests or by living or working in rodent-infested environments.
Exposure is more common in rural areas, but the Salt Lake County victim isn't believed to have traveled throughout the state and could have been infected within county lines, Baker said.
In North America there is no evidence of the virus spreading from human to human, according to the Centers for Disease Control and Prevention.
Infection can lead to respiratory failure or Hantavirus Pulmonary Syndrome (HPS), a deadly lung disease with a mortality rate of 38 percent.
"It's really rare, but potentially deadly, which is why we want people to be aware of their surroundings," Baker said.
Rodent populations fluctuate. But weather, particularly a dry spell followed by a period of heavy rain, can increase a person's chances of exposure to hantavirus, said Hector Aguilar-Carreno, a researcher and assistant professor at Washington State University's Department of Veterinary Microbiology and Pathology.
Rain feeds the crops, which fuels the mice population, increasing the likelihood of their spreading the pathogen, he said. When the weather warms, contaminated particles are more easily disturbed and sent airborne.
To avoid exposure health officials recommend that residents wear a mask, glasses and rubber gloves when cleaning up rodent urine and droppings.
Do not sweep out infested areas. First soak the droppings in disinfectant or a mixture of bleach and water for five minutes, then use a paper towel to wipe it up. Finally, mop the area with a bleach solution and wash hands with soap and warm water.
The recommended cleaning solution is a mixture of 1½ cups household bleach and a gallon of water. A smaller amount can be made with one part bleach and 10 parts water.
Early detection of symptoms and treatment by a doctor are also key, Baker said.
Hantavirus symptoms generally begin with a fever greater than 100.5 degrees, muscle aches, and chills. Other common symptoms include coughing, shortness of breath, nausea and vomiting, diarrhea and headache. Less common symptoms are dizziness or a light-headed feeling, sweating, and joint, back, chest, or abdominal pain.
There have been 587 reported cases of hantavirus in the U.S. from 1993 to 2011, with three-quarters of the victims living in rural areas. Here are the numbers for western states:
Arizona • 65
California • 52
Colorado • 76
Montana • 32
Nevada • 24
New Mexico • 89
Texas • 38
Utah • 25
Source • U.S. Centers for Disease Control and Prevention