SAN FRANCISCO (CBS SF) — A local health official warned on Friday that the latest spike in COVID-19 cases is edging San Francisco towards the purple tier, where the city could end up by the weekend.

San Francisco Public Health Director Dr. Grant Colfax was speaking during the latest update on the city’s response to the coronavirus pandemic Friday afternoon. While San Francisco currently remains outside of the area impacted by the state-ordered curfew, that could change if cases continue to rise.

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“SF is in the red tier and not immediately impacted by the order. However, our trajectory could have us in the purple tier as early as Sunday,” explained Colfax. “At that point we will need to abide by the shelter-in-place order.”

He noted that San Francisco’s case numbers had quadrupled over the past few days.

“The week of Nov. 16, we had 768 newly-diagnosed cases of COVID-19 in San Francisco,” said Colfax. “If we continue on this trajectory, a nearly quadrupling of cases over a month, our health care system could soon be struggling to deal with the burden of the virus and we will have many more people in the hospital diagnosed with COVID-19.”

Colfax warned that the latest increase was at a higher rate than San Francisco had experienced since the pandemic started.

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“Unfortunately, here in San Francisco, we are seeing an increase in our cases. We are in a surge that has the potential to overwhelm our local health care system, further reverse our reopening, and force us back to shelter-in-place,” said Colfax. “Since the beginning of October we have experienced a steep increase in our rate of cases. Importantly, this rate of increase is higher than we experienced during our summer surge of cases.”

When asked how quickly San Francisco would join the current curfew order for all California counties at the purple tier if the city’s case number placed San Francisco on that tier this Sunday, Colfax said, “We’re getting clarification from the state on that, but it would be relatively soon if we are moved into the purple tier by the state. I just want to be clear we are not absolutely confident that that would happen this Sunday, but it could happen as quickly as Sunday.”

He noted that the city would probably implement the curfew within 48 hours.

Colfax said that if San Francisco residents insist on gathering for the holiday despite his strong recommendations against it, they should limit those gatherings to only six people. outdoors with masks on.

“The choices we, you, I make in the next two weeks will determine the trajectory of this holiday season,” Colfax said. “The safest way to celebrate Thanksgiving is to stay at home with members of your own immediate household.”

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Additional information on the current status of the COVID-19 pandemic in San Francisco is available on the city’s coronavirus website.