California moved more counties to tighter restrictions on business and activities Tuesday after the state set new records of daily infections amid a relentless autumn surge that has left health officials pleading with people to avoid Thanksgiving gatherings outside their households this week.

One local health chief even went so far as to admonish the public for behaving “selfishly.”

Health departments around the state reported 20,554 new coronavirus cases Monday, shattering the previous single-day record of 16,521 that followed the July 4 weekend. That brought the state’s daily average of new cases to a record 12,442 over the past week, doubling in the span of 12 days.

Health and Human Services Secretary Dr. Mark Ghaly said Tuesday the new infections generally are linked to social gatherings in which people remove face masks and are close to others outside their households. All counties report that private gatherings are significant drivers of infections, though not necessarily the biggest, he said, while others point to restaurants.

“We are truly in the midst of a surge here in California,” Ghaly said. “I can’t put my finger on the exact source of transmission. The truth is, because of the way people gather, any activity that allows us to take our guard down is going to become a potential transmission risk.”

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Seven counties moved to higher-tier restrictions Tuesday in the state’s four-color reopening scheme: Colusa, Humboldt, Del Norte and Lassen bumped up to the highest purple tier for widespread infections, Calaveras to the red tier for substantial cases, and Alpine and Mariposa to the orange tier for moderate spread. No counties remain in the yellow tier for minimal transmission.

Statewide, 45 of 58 counties that are home to 95% of Californians now are under the purple-tier restrictions including most of the Bay Area — with retailers limited to 25% capacity and indoor activity banned at gyms, theaters, museums and worship places.

San Francisco, San Mateo and Marin counties avoided a move to the purple tier Tuesday, but officials warned that outbreaks remain dire and urged people not to become complacent. Dr. Grant Colfax, San Francisco’s public health director, said the city is “fast approaching the case count to be reassigned to the purple tier,” with an infection rate expected to surpass its summer peak “in the coming weeks.”

“While this is still lower than the national and state average, we are at a critical moment,” Colfax said. “We can’t let the virus get so far ahead of us that we can’t catch up.”

San Mateo County Health Officer Dr. Scott Morrow was far less gentle in a statement Monday, urging residents to abide by public health orders to avoid new infections and restrictions.

“Right now, enough people are acting like they are individuals, carelessly, thoughtlessly, and I would add quite selfishly, whether by intent or not, resulting in a surge in new cases,” Morrow said. “Because of these actions, everyone’s lives are disrupted, schools will not function properly, and your favorite businesses will close, likely forever. The holidays are going to be a super critical time.”

San Francisco had advanced to the least restrictive yellow tier for minimal outbreaks Oct. 20, the only urban county to do so. At the time, only a dozen California counties remained under the purple restrictions for widespread outbreaks — in Los Angeles, as well as counties with significant agriculture in the Central Valley, Inland Empire and Central Coast, including Sonoma and Monterey.

But since then, the turnaround in infections, hospitalizations and now COVID-related deaths has been dramatic.

The state processed more than 283,000 tests on Monday, and has seen its two-week average rate of positive test results rise 51% since Nov. 10 — from 3.7% to 5.6%, Ghaly said. Hospitalizations have risen more than 81% over the last two weeks to 5,844, Ghaly said. Intensive care hospitalizations, he said, are up 57% over two weeks to 1,397.

“Hospitals are stretched,” Ghaly said.

Those figures are only likely to worsen with rising cases, Ghaly said. The state’s daily reported case totals differ slightly from numbers that news organizations compile from county health departments but follow the same trends.

Ghaly repeated his plea for Californians to avoid indoor Thanksgiving gatherings beyond their households to avoid making the case surge worse, even suggesting, with fair weather in the forecast, that they consider an outdoor Thanksgiving lunch instead.

“I, like many of you, am disappointed at how this Thanksgiving will look compared to years past,” Ghaly said. “This year it will look different for me and my family, I’m hoping it will look different for you and yours as well. The safest way to celebrate is at home with members of your household.”