A middle-aged man died from the A/H1N1 virus, bringing the death toll in California to four, local authorities said Monday, Xinhua reported.
The victim was also the first person killed by the disease in Orange County near Los Angeles, according to the Orange County Health Care Agency.
As of Monday, Orange County has reported 86 confirmed and suspected cases. While across California, there has been more than 1,000 confirmed and suspected cases, said Deanne Thompson from the agency.
But he said the 86 cases in Orange County are probably just a small portion of the real number.
"We're not testing for every (suspected) case anymore," he said.
Instead, the health agency, whose lab has been certified to conduct such testing, is examining only severe cases or those representing clusters in such areas as schools or workplaces.
"We believe that greatly underestimates the number of cases," he said. "We know transmission is continuing."
The county's health officer Eric Handler said the man's death "is a sad reminder of the serious threat posed by the A/H1N1 influenza and other influenza viruses."
"It is important for everyone to continue practicing good respiratory and hand hygiene to limit the transmission of influenza germs," Handler said.
There is currently no vaccine available to protect against the virus, but people can take steps to prevent the spread, such as washing hands often with soap and water and coughing or sneezing into a tissue or into one's elbow, Thompson said.
The symptoms of the A/H1N1 flu are similar to those of seasonal flu and include fever, sore throat, body aches, headache, chills and fatigue.