On the morning of March 15, as Italy became the epicenter of the global coronavirus pandemic, a half dozen high-ranking California health officials held an emergency conference call to discuss efforts to contain the spread of the virus in the San Francisco Bay Area.

The tight-knit group of Bay Area doctors organized the call to discuss a consistent policy on public gatherings for the region’s 7 million people, which then had fewer than 280 cases and just three deaths. Soon, though, the conversation focused on the potentially catastrophic emergency on their hands and how stay-at-home orders could slow the advance of the virus.

Many factors have fueled the speed of the disease spread throughout the world. But that three-hour call and the bold decisions to come out of it were central to helping California avoid the kind of devastation the virus wrought in parts of Europe and New York City, experts say.

“It was obviously spreading like wildfire under our noses and literally every minute we did not take aggressive action was going to mean more and more death,” said Dr. Scott Morrow, health director for San Mateo County, just south of San Francisco and home to Facebook.

To get a sense of just how much the novel coronavirus has changed life in the Bay Area, we decided to fly a drone over some recognizable spots across the region. Take a look at what we found.

The doctors who met that day are members of the Association of Bay Area Health Officers, a group born out of the AIDS epidemic that ravaged San Francisco in the 1980s. The group usually meets a half-dozen times a year and has tackled other global threats such as Ebola and swine flu.

By mid-March, group members were alarmed by the spread of the virus since an initial case in the state was confirmed Jan. 26. Dr. Sara Cody, the top doctor in Santa Clara County, home to 2 million residents and the headquarters of Apple and Google, told her peers that COVID-19 cases were doubling every three days. In neighboring San Mateo County, every test conducted was coming back positive, shared Morrow. Across the bay in Alameda County, Dr. Erica Pan reported that cases were rising in areas bordering Santa Clara County.

A day later, the San Francisco Bay Area became the first place in the nation to order residents to stay home. At least 20 other California counties adopted the Bay Area order within hours. Two days later, Gov. Gavin Newsom ordered all 40 million Californians to stay home unless they had essential jobs.

It’s impossible to quantify how much those orders helped or truly compare states or countries because of other potential factors such as population density, international travel and the number of tests being conducted in each place. However, experts in disease control say the Bay Area’s early intervention clearly played a significant role in slowing the speed of infection throughout California.

On March 15, California reported 335 cases and six deaths. As of Sunday morning, the state had confirmed more than 30,800 cases and nearly 1,150 deaths. The slowing rate of infection, at 73 per 100,000 residents as of Friday, and deaths is one one of the reasons Newsom says the state can contemplate reopening businesses.

The area is now reaping the benefit of putting stringent recommendations in place “very, very early,” said Robyn Gershon, a clinical professor of epidemiology at New York University’s School of Global Public Health.

“In New York, by the time social distancing came we already had many, many people sick. Without tests, without a vaccine, your only tool is having people not contact each other,” Gershon said.

Just a few days after California’s order, with the number of infections above 15,000 in New York state and more than 100 dead, New York Gov. Andrew Cuomo ordered businesses and workplaces to shut down.

Most people recover from the new coronavirus with symptoms such as fever and cough that clear up in two to three weeks. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, and death.

In January, the group in California began holding twice weekly phone calls to prepare for coronavirus, initially discussing how to monitor Americans returning from China, where the virus began, or how to disinfect ambulances that had transported COVID-19 patients.

But on March 15, the call focused on “extreme social distancing.” Marin County Public Health Director Dr. Matt Willis wondered whether such a radical measure was needed in his county, which at the time had only 10 cases. But with no federal or state guidance, he soon agreed “an aggressive approach to a shelter-in-place policy was really the one lever that we had.”

Cody, who has been credited by many for driving the urgency during that call and whose county was the first to declare a state of emergency in California, told colleagues of increasing hospitalization rates there, sharing early data from a Centers for Disease Control and Prevention community survey that found about one in 10 of those seeking medical care for flu-like symptoms at public clinics had coronavirus.

“We realized we were not that far behind what was happening in Italy,” the Santa Clara County health director said.

On March 15, Italy’s hospitals were already overwhelmed, with more than 1,800 having died. Less than a week earlier, officials had imposed countrywide, strict stay-at-home orders after they failed to contain the outbreak in the hard-hit north. The death toll has now climbed to nearly 23,000. The European country had confirmed its first two cases on Jan. 31.

Officials have contemplated why San Francisco Bay Area residents have largely complied.

Californians were already seeing daily images of a cruise ship off California’s coast with at least 21 confirmed coronavirus infections aboard before it docked on March 9, so the virus was front-of-mind. Tech conferences that typically bring international travelers to the Bay Area each spring were being canceled and tech companies from Silicon Valley to San Francisco began telling employees to work from home. It’s also the makeup of the Bay Area, officials say, including people with connections around the country and world.

San Francisco residents generally are willing to comply with such things “when shown the science, when shown the data about what can be accomplished,” said Dr. Susan Philip, director of disease prevention and control at the San Francisco Department of Public Health.

In the month since, Bay Area residents have largely continued to heed the mandate, quickly understanding the concept of “flattening the curve” to slow the rate of infection and avoid overwhelming hospitals.

“The timing of instituting the stay-at-home order is very, very critical in blunting the epidemic,” said Lee Riley, a professor of epidemiology and infectious diseases at the University of California Berkeley. He warned, though, that complacency could ruin any initial success, noting “we need to remain vigilant.”

Still, a challenge looms for the Bay Area doctors who continue to talk to each other twice a week: How to lift the shelter-in-place orders without creating a second surge.

“We’re going to be relying on the same kind of partnership that we relied upon for the first stage of this to help us through,” Willis said.

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Associated Press writer Jocelyn Gecker contributed to this report.