Sonoma, Marin, Napa, Solano, Mendocino, 8 other California counties move to CDC’s ‘high’ COVID level. Is it mask time again?

The U.S. Centers for Disease Control and Prevention on Thursday placed more than a dozen California counties into the “high” community level for COVID-19 danger.

Thirteen California counties were placed in the high level: Del Norte, El Dorado, Marin, Mendocino, Monterey, Napa, Placer, San Benito, Santa Clara, Sacramento, Solano, Sonoma and Yolo counties.

That means federal health officials are calling for people in those counties to mask up in public indoor settings.

Alameda County health officials on Thursday announced a new indoor mask mandate would take effect at 12:01 a.m. Friday. Alameda was not among the counties moved into the CDC’s high level Thursday, staying in medium, but it was near the data thresholds for the high level based on recent hospitalizations.

It is not yet clear whether any other health offices in the Bay Area or Sacramento area are planning to join Alameda County in returning to a countywide mask order.

Sonoma County spokesperson Matt Brown said the county is not currently considering an indoor mask mandate but Health Officer Dr. Sundari Mase is monitoring the situation and in touch with other Bay Area health officers and would reassess as needed.

“We continue to monitor cases and the impact on hospitals,” Sacramento County health spokeswoman Samantha Mott said in an emailed response Thursday. “Public Health continues to strongly recommend vaccination and wearing masks in public places.

“Businesses may make independent risk assessments and implement additional requirements such as masking.”

Data behind CDC’s community level assignments

The CDC considers per-capita case rates as well as hospitalization metrics in its community level assignments, calculated weekly on Thursdays.

Any county with at least 200 weekly cases per 100,000 residents is moved at a minimum into the “medium” level of the three-tiered framework.

Counties with a case rate above 200 are then moved into the high level if their corresponding health service area – groups of counties that share hospital resources – records a weekly total of 10 or more COVID-19 hospital admissions per 100,000 residents, or if the health service area has 10% or more of its staffed hospital beds occupied by virus patients.

The CDC as of Thursday recorded Sonoma County at 299 cases per 100,000 for the past week, Solano at 272, Marin at 400, Napa at 257 and Mendocino at 206.

COVID-19 hospital admissions per 100,000 for the week were 11.8 in Sonoma, 11.5 in Solano, 11.8 in Marin, 11.5 in Napa and 13.8 in Mendocino.

Lake County was in the “medium” community level last week, with 191 cases and 11.5 COVID-19 hospitalzations per 100,000.

San Francisco and San Mateo counties were on the cusp of the high community-level threshold, both measured at 9.6 hospitalizations per 100,000, up from 8.2 last week. Alameda and Contra Costa counties were also close at 9.3 per 100,000, from 7.3 last week.

Up until Thursday, none of California’s 58 counties had been in the high level since recovering from winter’s omicron surge earlier this year.

The upgraded risk levels reflect a surge of COVID-19 sweeping through most of the U.S., largely fueled by more contagious offshoots of the omicron variant. One of those subvariants, BA.2.12.1, recently became dominant both nationwide and within the CDC region that includes California.