If you're heading to a 49ers playoff party Sunday, watch out for uncovered coughs: California is now officially experiencing widespread flu activity.
The Golden State reached that designation Friday, joining 47 other states with widespread aches, fevers, runny noses and general misery.
Usually the flu season doesn't peak here until late February or March, about the time the A's and Giants head to spring training.
So this could be a sign of an especially severe season, or simply an earlier-than-normal one. Only time will tell, said Dr. Gil Chavez, deputy director of the Center for Infectious Diseases at the California Department of Public Health.
As of Friday, five people younger than 65 have died in the state so far this season, and flu-related hospitalizations and doctor visits are higher than normal for this time of year.
The state does not track deaths in people over age 65. But Santa Clara County health officials reported this week that a 98-year-old woman died from flu complications earlier this month.
"It's a bad year for the elderly," said Dr. Tom Frieden, director of the national Centers for Disease Control and Prevention, in a conference call with reporters.
Does that mean 49er fans should skip the parties and hunker down at home?
Only if you're sick yourself, experts advise.
But there are steps you can take to protect yourself from Aunt Mary sneezing up a storm, or little Bobby running around touching everything, notes Charles Chiu, an infectious disease physician at UC San Francisco, who plans to attend a party himself.
Topping the list is a flu shot -- if you've already had one. This year's vaccine is a good match for the circulating flu strains, especially the predominant one -- influenza A H3N2 -- which often causes more serious illnesses and hospitalizations than other strains.
Getting a shot on Saturday won't help for Sunday's party because it takes about two weeks to develop immunity. But it should be effective in time for that big Super Bowl gathering.
California has received 18 million doses of flu vaccine, and while some pharmacies, health care providers and others have had spot shortages, most have been able to quickly order more, Chavez said.
The flu shot is no sure thing. Most of the time it protects, but not always. Federal health leaders estimate this year's vaccine is about 62 percent effective, so it's wise to take other precautions, too.
The most common way the virus spreads is through the droplets that spray out as sick people cough or sneeze. Or cheer.
Those droplets can lodge on doorknobs, TV remote controls and other surfaces and remain viable for at least four hours, or as long as 12 to 24 hours, Chiu said.
He advises people to shake hands upon entering a room, if that is your habit, but then wash your hands with soap and water for at least 15 seconds before diving into the hot wings or guacamole dip.
"Don't walk in and sit on the couch and grab some chips," he said.
Washing your hands frequently throughout the day, and avoiding touching your face so you don't breathe in the virus, are some of the better ways to protect yourself.
Unlike the norovirus, which often spreads through food, the flu virus is primarily spread when it is airborne or on hard surfaces, Chiu said.
And if one of your fellow partygoers is sneezing and coughing profusely? Chiu advises people to stay at least 6 feet away.
"Unfortunately, the measures do conflict with societal niceties," he admitted.
Wash your hands before leaving the party, Chiu suggests, to avoid bringing the virus back home.
And think about your fellow partygoers if you're the one hosting. "If you're sick," he said, "you really don't want to prepare the food."
Sandy Kleffman covers health. Contact her at 510-293-2478. Follow her at Twitter.com/skleffman.