Garrett Chase, 21, died Monday, just a few days after he was taken to a hospital for vomiting and diarrhea.
Lab tests done by the state Health Department confirmed the presence of hantavirus on Friday, said Peter Browning, director of the Skagit County Health Department.
The hantavirus infection is spread by the common deer mouse.
"It's pretty rare for this area," Browning told the Skagit Valley Herald. "We knew it was in the mouse population a while ago, and we can assume there were cases in the past, but none verified by a lab."
County health department investigators hope to identify where Chase may have been exposed to the virus. Because the disease cannot be spread through human contact, local residents should not become alarmed, Browning said.
"It's very difficult to talk to the family at this point about what might have happened," he said. "I think we'll wait until next week to pursue where he may have got it. If it were a communicable disease, we would be much more aggressive."
Hantavirus pulmonary syndrome also is characterized by fever, chills and severe muscle aches, followed by difficulty in breathing and shortness of breath.
Deer mice are the main carriers of the deadly virus, which kills 40 percent of people infected. Because the virus is present in mouse droppings, urine and saliva, the disease can spread to humans who are exposed by breathing dust after cleaning or working in areas where rodents are present.
Migrant workers and people who work around barns where deer mice may be present are among those most at risk for contracting the virus, Browning said.
Chase was a student at Skagit Valley College.