How long will it take for the Bay Area to 'come down the curve' of the coronavirus pandemic

A woman in a face mask walks by a sign posted on a boarded up restaurant in San Francisco, California on April, 1, 2020, during the novel coronavirus outbreak. A woman in a face mask walks by a sign posted on a boarded up restaurant in San Francisco, California on April, 1, 2020, during the novel coronavirus outbreak. Photo: JOSH EDELSON/AFP Via Getty Images Photo: JOSH EDELSON/AFP Via Getty Images Image 1 of / 74 Caption Close How long will it take for the Bay Area to 'come down the curve' of the coronavirus pandemic 1 / 74 Back to Gallery

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Models projecting the course of the coronavirus pandemic usually display something resembling a symmetrical bell-shaped curve, which indicates that the amount of time it will take to "come down" the curve will be the same as the time it took to approach the peak.

With evidence suggesting the San Francisco Bay Area may be peaking this week and California Governor Gavin Newsom set to announce the state's plan for reopening Tuesday, the question on many minds is just how long it will take before shelter-in-place orders can be lifted.

UCSF epidemiologist Dr. George Rutherford believes the bell curve is not symmetrical and will have a "long tail" on the way down.

“If this were a totally unperturbed biological system, there’s some logic in expecting to see a symmetrical expansion and contraction of infection," he said. "But this is not an unperturbed biological system. We are doing all sorts of things to limit transmission, whether it's shelter in place, wearing masks, eliminating transmission in hospitals, all the things we’re doing to screw up the virus. As a result, the curve is going to have a jagged peak and long tail down, reflecting it hitting a wall of humans not cooperating.”

Intuitively, one may be led to believe that aggressive social-distancing measures would prompt the curve to decline precipitously on the way down, since the pre-peak portion of the curve was comprised of pre-social distancing transmission and the latter portion of the curve is comprised of limited transmission due to social distancing. However, while the transmission on the curve's downward-sloping portion is limited, there's enough of it to ensure a "long tail" before coming back down to zero.

“There’s plenty of residual transmission if you think of being sheltered in place with other people," Rutherford said. "In some cases, people are sheltered in place with eight roommates, and then you have health care workers bringing it home and people coming from the outside that haven’t been socially distancing bringing it in to the community. You also have essential workers running cash register at Safeway potentially getting the virus, which will contribute to smaller chains of transmission and a much larger tail.”

Will this long tail stop the region from reopening when it gets far enough away from the peak? Rutherford doesn't believe this will be the case, citing the four criteria laid out in a widely circulated American Enterprise Institute report.

"The four criteria are low rates of transmission, huge testing capacity, very robust contract tracing and available hospital beds, but I'd add a fifth thing: Strategy to maintain social distancing short of shelter in place," he said. "So masks, restricting large gatherings, et cetera."

Rutherford stated that the Bay Area has "plenty" of hospital beds, and added that he expects widespread testing and a workable contact tracing policy to be in place in three to four weeks. As for when the rate of transmission is sufficiently low, Rutherford is particularly sanguine.

"It may well be right now," Rutherford said, in reference to the region's encouraging hospitalization data and the leveling off of new cases. "I just don’t know and we can’t prove it just yet. Measuring how much transmission is falling is not easy as you're mostly looking at the cases reported, but you can also look at the number of people admitted to hospitals."

UCSF is working on a number of reports and plans for measuring transmission as well as the implementation of contract tracing, which will involve each locality putting together a task force of workers who will keep tabs on each new case and work to test and quarantine close contacts. Rutherford stated that all the information Newsom needs before deciding to pull the trigger on reopening should be available in the not-too-distant future.

"Contact tracing will be robust, testing capacity will expand, and we may be in a position to make an informed decision relatively soon," he said. "But it's not my decision, the governor will make it, county and city governments will make it, and they will want as much data as possible."

If contact tracing is done effectively and precautions such as masks in public and bans on large gatherings remain intact, Rutherford is optimistic the Bay Area won't ever have to return to shelter in place. However, if the virus is not contained in other locations and brought back to the Bay Area by travelers without anyone realizing it, that could change things.

“That’s the real question," he said of potential travel restrictions across the state and country. "How do you do this piece-meal? What’s to stop a plane from Dallas with 50 people positive coming in because they did not shelter in place long enough? How do we maintain our island status?”

In any case, policymakers will have to find a way to strike a delicate balance between mitigating economic damage while still keeping the virus on a steady "long tail" with no dramatic increases. The worst-case scenario would be a second wave that prompts officials to call for the return of stay-at-home orders.

"I don’t know that people will have great tolerance for it," Rutherford said of another round of shelter-in-place. "We have to try not to get back into it since even though it works great for disease control, it does not work great for economics."

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Eric Ting is an SFGATE digital reporter. Email: eric.ting@sfgate.com | Twitter:@_ericting