A 30-year-old Coachella Valley man who died at a hospital this week tested positive for the H1N1 virus, according to the Riverside County Health Department.
The case marks the first influenza-related death of the flu season in Riverside County, health officials said. No other details about the man were released.
Officials said they're looking at whether other health problems contributed to the man's death, and if he received a flu shot. The vaccine helps guard against the 2009 H1N1 strain.
Commonly called swine flu, the virus that emerged in 2009 affected mostly children and young adults. The virus was responsible for many deaths across the world until 2010, when the World Health Organization officially declared the pandemic over.
But three years after the outbreak, California state health officials say reports of H1N1 in the state on the rise again.
Riverside County health officials said they have seen some recent increases in instances of flulike illness, but overall flu activity is at expected levels for this time of the year.
Officials say the most effective protection against the flu virus is getting vaccinated. The Centers for Disease and Control and Prevention recommends that all people 6 months and older receive flu vaccinations every year.
"Some people wrongly believe that is too far into the flu season," said Dr. Cameron Kaiser, Riverside County's public health officer. "That is not the case. There is still time and the vaccine is readily available."