It’s been more than nine months since California required face masks indoors in public places to slow the spread of COVID-19. But with cases spiking again during the winter holiday season, is there anything that could trigger a return of the mask mandate?

State health officials considered it an “important tool” in keeping the virus from overwhelming hospitals, which are seeing a rise in cases — but nothing, so far, like last winter’s record numbers.

For now, masks remain optional indoors — but highly recommended — in most public places. But the latest spike in infections already has sparked a stepped-up indoor mask requirement in some settings under state law. Here’s a quick look at what the current rules say.

Q When did California last require wearing masks indoors?

A One year ago this week the state reinstated its general indoor face mask requirement amid a sharp rise in cases from the super-contagious omicron variant. Masks were required in indoor public places and businesses — retail, restaurants, theaters, family entertainment centers, meetings, state and local government offices serving the public. That requirement lifted March 1 for most public settings and March 11 for schools and childcare. The mask requirement for public transit and transit hubs lifted April 20.

Q Are there places where the state continues to require masks indoors?

A Yes. Mandates have remained in effect for healthcare, long-term care and adult and senior care facilities.

Q Do other places have indoor mask requirements that kick in when cases get high?

A In several Bay Area counties — Santa Clara, Alameda, Contra Costa, Solano and Napa — masks now are required again for jails, prisons and detention centers, homeless or emergency shelters and cold-weather shelters. That’s because those counties have reached the Centers for Disease Control and Prevention’s medium or high community risk level, at which state law requires masks in such high-risk settings. The law allows masks to be optional in those settings for counties in the CDC’s low community level.

Q What is a “community risk level”? Where can I find the current level for my county?

A The CDC introduced the community level metric in March, based both on case rates and hospitalizations to reflect the virus’ impact on the regional health care system. The CDC maintains an online map of the country listing the risk level in every county. It currently shows Santa Clara County in the high risk level, Alameda, Contra Costa, Solano and Napa counties in the medium level, and San Mateo, San Francisco, Marin and Sonoma counties in the low level. The levels are updated on Thursdays.

To be clear, that metric isn’t the same as the CDC’s transmission level, which is based on case rates and positive tests, but excludes hospitalizations. The transmission level is high in every Bay Area county and across most of California, but it’s not the metric that would trigger new mandates.

Q What are the chances California will reinstate the statewide general indoor mask mandate?

A That’s unlikely anytime soon. The state health department said Monday that “we are not considering a statewide masking mandate at this time” and “we are empowering Californians to take voluntary actions, including masking in public indoor settings, and getting the flu shot and updated COVID-19 booster, to protect themselves and their families from multiple respiratory viruses circulating in the state.” The department noted, however, that “local governments may implement separate and more strict policies.”

Q But aren’t we in a case surge like last winter?

A It’s hard to compare. Reported case counts and infection rates are a fraction of what they were in January, but so is the amount of daily testing reported to health agencies. Many people with mild COVID aren’t testing at all and those who do often use at home rapid antigen tests and don’t report the results. So while health authorities say cases are higher than reported, they don’t know by how much.

Q Are there local mandates that would go beyond the state’s limited requirements?

A Bay Area county health officials say they aren’t planning to renew an indoor mask requirement for now, even with cases rising sharply, though they strongly recommend masks not only to protect against COVID-19 but also influenza, which is circulating early this year. They note that vaccines are available that help protect against both.

BART’s governing board has said the transit system will require indoor masks if a local health officer reinstates indoor masking in any of the five counties served by BART (Alameda, Contra Costa, San Francisco, San Mateo, Santa Clara), or if the state or federal government mandates it. It also could require masks if “any U.S. metropolitan area outside the Bay Area experiences a COVID-19 surge as defined by the CDC,” meaning any spike in case reports that may “overwhelm the local points of care.”

Q Will mask mandates appear in other counties?

A Los Angeles County has a policy that would reinstate the indoor mask mandate if the county remains in the CDC’s high community level for at least 14 straight days. But county health officials believe that may not happen.

Q What about cities?

A Cities can impose their own COVID mandates too, though only the largest tend to do so. Oakland on Nov. 1 lifted its mask requirement for indoor gatherings of 2,500 or more people, and on Nov. 28 eliminated a requirement to mask in city libraries, recreation centers and civic center buildings. That last move drew a protest Tuesday by advocates for the disabled and elderly, who want the mandates to continue. San Jose does not currently have any requirements or mandates for masks at City public facilities.