The man died during the week of July 26 at a local hospital. It was confirmed Friday that he had the H1N1 virus, Napa County public information officer Elizabeth Emmett said.
The man had no other underlying medical conditions "that we know of," Emmett said.
"We are saddened by the death of a member of our community and our sympathies go out to his loved ones," Napa County Public Health Officer Dr. Karen Smith said.
"This is an unfortunate reminder that, although most cases of H1N1 have recovered without medical treatment, all flu viruses can be deadly and we must continue to be vigilant in preventing the spread of H1N1 and seasonal influenza," Smith said.
There have been at least 80 deaths associated with H1N1 infection in California and 353 deaths across the country, health officials said.
Napa County and surrounding counties have seen an increase in influenza-like illnesses over the past month, Smith said in a news release.
There are thousands of H1N1 cases in California, with the vast majority of patients experiencing mild to moderate symptoms and full recovery, Smith said.
A vaccine for the H1N1 flu is currently in production, with distribution expected in the fall. Napa County public health officials will provide more specific information as it becomes available, Smith said.
The symptoms of the H1N1 flu are similar to those of seasonal flu.
They include fever, a cough, sore throat, body aches, headaches, chills and fatigue. Some patients also reported diarrhea and vomiting, health officials said.
Those sick with flu-like illness are advised to stay home for seven days after symptoms begin or until they have been symptom-free for 24 hours, health officials said.