A closure sign in San Francisco's Marina district. Getty Images

In San Francisco, once feared to be a hotbed for the coronavirus, doctors are not yet seeing the dire overcrowding of hospitals that areas such as New York are experiencing. "I was on campus today, and it's actually quite mellow," said Dr. Bob Wachter, professor and chair of the Department of Medicine at UC San Francisco, told CNBC on Thursday. "Because we're not doing elective procedures that can be pushed back, it's even quieter than usual." For now, UCSF clinicians are managing a steady trickle of patients entering the emergency rooms with COVID-19 symptoms, while still bracing for a possible flood. As of Friday, San Francisco has 279 confirmed cases, and the city saw its largest increase of COVID-19 diagnoses on Thursday. California now has more than 4,000 known COVID-19 cases. At UCSF's Parnassus campus, there were 11 patients diagnosed with COVID-19 as of Thursday, seven of them in intensive care, according to Wachter who has made it a point to make that information available to the public. In preparation for a potential surge, the hospital has scaled down surgeries to only those that are essential, making it less busy than in the months before the pandemic. Wachter said he personally visited the Parnassus hospital on Thursday, and noted that the hospital's intensive care unit is still filled with empty beds and the emergency room is only "moderately busy." Moreover, the UCSF clinics have dialed down the volume of patients, with more than 50% of encounters now taking place online between doctors and patients. Because the number of seriously ill COVID-19 patients has been increasing at a manageable rate, the hospital has had more time to prepare. Infectious disease experts say that the region's early steps, including ordering people to avoid crowds and shelter in place, may have slowed the trajectory of the virus. But experts say it remains critically important that residents continue to heed the advice of public health officials and stay home. Wachter said he could see the situation take a dramatic turn for the worse at any moment and his team is watching closely for any signals. In the past few days, some medical experts, like the cardiologist and researcher Dr. Eric Topol, have noticed by studying the data that California appears to be taking a turn for the worse. "Their (California's) death curve slope is heading north, whereas it was more akin to Washington until the last 48 hours," he noted.

San Francisco residents have been sheltering in place for more than a week Jarred Colli

Wachter stressed that it's vitally important that residents continue to take the pandemic threat seriously. If the lockdown doesn't continue, people with mild COVID-19 symptoms, or those with no symptoms at all, could infect others at a rapid clip. California has only tested half as many residents as has New York, administering just over 66,000 tests as of midweek. That's far from enough. Similarly, San Francisco Mayor London Breed has pleaded with residents to act responsibly in public settings and threatened to take more drastic steps if needed. "I'm far from ready to declare victory," said Wachter. "But it is not too soon to say that there is a meaningful and statistically significant difference between San Francisco and New York."

Early steps

New York City now has more than 25,000 confirmed COVID-19 cases, and deaths in the state have topped 500, according to a briefing Friday by New York Gov. Andrew Cuomo. The true numbers of cases could be far higher given the lack of testing. The situation has become so overwhelming in New York that at some hospitals, patients are getting transferred to other facilities. Physicians have described the situation inside hospitals as "apocalyptic," with patients dying while waiting for a bed and doctors struggling to make do with limited numbers of ventilators. While true numbers are hard to gauge in either city, public health experts are already investigating why the number of patients sick enough to head to emergency rooms in San Francisco seems to be growing linearly, rather than exponentially. Two weeks ago, the two cities had roughly the same number of known cases. tweet One theory, according to Wachter, is that the Bay Area was early to restrict people from gathering in large numbers. San Francisco banned gatherings of more than 1,000 people on March 11 and joined five other Bay Area counties on March 16 as the first region in the U.S. to order residents to "shelter in place," that is, avoid leaving their homes except for essential business such as grocery shopping and medical visits. On March 19, the entire state of California followed suit. Another factor is that San Francisco is less dense and less populated than Manhattan, so its residents have not been in such close contact. Moreover, in the Bay Area, some of the largest employers, such as Twitter, Facebook and Google took an early lead in asking their workers to work from home before the region mandated it. "I think we're seeing some early signs that San Francisco seems to be doing something that's working," said John Brownstein, an epidemiologist and professor of medicine at Harvard Medical School. "There's lots of factors for that, absolutely, but I think the interventions that were put in place early on in California compared to other parts of the country are having an impact."

'We can't celebrate anything yet'

Outside of UCSF's hospitals, doctors are reporting similar experiences. At San Francisco's California Pacific Medical Center, which is part of Sutter Health, there were 14 positive cases across the hospitals as of Thursday, according to Dr. Jeffrey Swisher, the chairman of the department of anesthesiology. Swisher said he still expects to see an uptick in the next week but he also has reason to hope that the "slope won't be as steep" as in New York. "We haven't seen the surge here yet," he said. "It doesn't look anything like New York."

Sign at the entrance to the Mission Bay campus of the University of California San Francisco (UCSF) medical center in San Francisco, California. Smith Collection/Gado/Getty Images

Stanford, in Santa Clara County, has been harder hit by the virus than has San Francisco. A memo shared with staff and summarized by an insider for CNBC shows there are 33 positive or suspected COVID-19 cases as of Wednesday. But in a more concerning sign, 25 health providers were cited in the document as having the virus, but some of them were likely quarantined at home rather than at the hospital. It is unclear if these medical professionals, half a dozen of them doctors, caught the virus at work. A Stanford spokesperson declined to comment on the total number of COVID-19 cases, noting that the "situation is fluid." In other parts of the state, the situation is similarly stable but doctors are unnerved about the potential for a shift at any moment. Dr. Ceasar Djavaherian, an emergency medicine physician, described an "eerie silence in the emergency rooms" when he was at the hospital on Monday at Northbay Health System in Vacaville, California. The hospital treated one of the first known coronavirus cases in the United States, and has seen several health workers likely infected. This week, Djavaherian said he's considered relocating to New York to help after talking to doctors there but has decided to stay put in San Francisco in case the situation worsens locally. Likewise, Dr. Ethan Weiss, a UCSF cardiologist and researcher who's been helping out at the Mission Bay campus, said the doctors there aren't seeing "much yet." But Weiss did say he went to one of San Francisco's most popular parks this weekend and saw young people ignoring the guidance by sitting closely together, socializing and drinking. "When I see that, I'm reminded that we can't celebrate anything yet."