SAN FRANCISCO (CBS SF) — With new COVID cases surging across the Bay Area, San Francisco and San Mateo counties were relegated Saturday from the Red Tier to the Purple Tier on the state’s COVID monitoring scale, triggering a new wave of restrictions on local businesses.

Marin remained the only San Francisco Bay Area county not in the highly restrictive Purple Tier.

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San Mateo County officials also announced a new stay-at-home order – prohibiting residents from leaving their homes to gather with other households from 10 p.m. to 5 a.m. beginning Monday night. During those hours, no gatherings are allowed among households, with certain exemptions.

Under Purple Tier restrictions, businesses and activities that may have been operating indoors in the county – including places of worship, movie theaters, gyms and museums – must move outdoors or close. Shopping malls and all retail must operate at no more than 25 percent capacity.

“We have not seen numbers like this in quite a while and we really need to reverse this incredibly troubling trend,” County Manager Mike Collage said in a news release. “What’s important to remember is that we can reverse the trend as long as we follow common-sense health and safety practices.”

San Mateo County health officials reported an approximately 85 percent spike in new COVID-19 cases from October to November. The rollback to Purple is due to the county’s new adjusted case rate of 7.6 per 100,000 population.

San Francisco health officials had taken to social media on Friday, warning that a move into the Purple Tier was imminent.

“Unfortunately, the number of tests (in the city/county) coming back positive in the last 4 weeks has increased 265%,” San Francisco Health Director Dr. Grant Colfax tweeted. “That means just in the last month, our positivity case rate was 0.81% and today is 2.15% and going up.”

The last time the San Francisco Health Department updated its public COVID dashboard was on Nov 25. At that time, there were 15,342 active cases in the city. The Mission and Bayview Hunter’s Point neighborhoods have been hit the hardest. The Marina District and Presidio Heights were just a notch below.

“The data are clear: the current surge of COVID-19 cases is more aggressive and widespread than we have previously experienced,” Colfax said in a news release. “We must take decisive action now — as a city and as individuals — to stay ahead of this virus. The assignment by the state to the most restrictive tier is indicative of how widespread this virus is. We need everyone to be diligent or a further roll backs of activities may be necessary.”

San Francisco officials also said they would be implementing stay-at-home order prohibiting residents from leaving their homes to gather with other households from 10 p.m. to 5 a.m. beginning Monday night.

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Additionally, health officials said all indoor worship, indoor movie theaters, indoor gyms and fitness centers and indoor operations at museums, aquariums, and zoos will be prohibited. All schools – TK-12 — that are already open for in-person learning may continue to offer indoor instruction.

“While the number of cases is increasing significantly, the people of San Francisco have shown they can take action and follow the guidance to get us through this pandemic,” said Mayor London Breed in a news release. “This is about protecting ourselves, our families, and our community, and getting us to a better place so we can get people back to work and support our small businesses. Every single person needs to do what they can over the next few weeks. The decisions you make today will impact where we are tomorrow.”

Colfax also issued a warning about the city’s testing capacity.

“Please do not use public testing resources in advance of engaging in behaviors that easily spread the virus. Namely to travel or to gather with people outside your households,” he said. “We must ensure that testing is available for those who need it most — for those who are sick, have had a high-risk exposure and those who have no other testing options.”

He also emphasized that a negative test was not a green light to engage in risky behavior.

“A negative test is simply not a ticket to freely socialize without precautions,” Colfax tweeted. “A negative test is not a ticket to mingle with extended family or friends outside of your immediate household.”

While the city has not implemented the kind of stay-at-home restrictions being enforced on Monday in Los Angeles, Colfax’s advice was very similar to his Southern California counterparts.

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“Your choices impact how the virus spreads — stay home as much as possible,” Colfax tweeted. “Do not gather with people you don’t live with.”