Dr. Bob Wachter is chair of the Department of Medicine at UCSF, one of the top medical schools in the country. He is a founder of the hospitalist field (doctors who provide general medical care to hospitalized patients) and is the author of several books, including “The Digital Doctor: Hope, Hype and Harm at the Dawn of Medicine’s Computer Age.”

The professor of medicine has emerged as a prominent national source for Covid-19 facts and analysis, tweeting science daily and hosting UCSF’s “Grand Rounds” videos on YouTube, where UCSF experts discuss the latest in epidemiology, virology and diagnostic testing.

He spoke with J. over the phone on May 1.

J.: How has the Bay Area done so far in battling the pandemic?

Dr. Bob Wachter: I think the first phase we should be incredibly proud of and pleased about. That’s always a hard thing to say when people die, so I don’t mean that in any kind of insensitive way. But considering what I thought was going to happen six weeks ago, and what we know now could have happened as we look at New York, we had a remarkably benign first wave. And that was sort of amazing, and truly wonderful. We saved thousands and thousands of [people] who would have died had we not responded in the right way.

Last month was in some ways brutally hard and remarkably easy, in a way, because it was straightforward. It was essentially lockdown, and that’s it. The next phase is wildly complicated. Trying to figure out, are we in a place where we can open? And if the answer is yes, how much and for who? Who can go out and who shouldn’t? And how essential is a business? And how long should this phase be, and what are the metrics we’re going to look at to see whether we chose right or wrong? It’s really, really complicated.

A few weeks ago you were saying that San Francisco was beating the odds in terms of keeping the number of cases down. How do you see it now?

I’d say the state of the virus in San Francisco is not as wonderful as I would have hoped and maybe expected. In other words, the trajectory we were on a couple of weeks ago was one in which it was really kind of a mild number of cases in San Francisco, and it was going down every day. The last week or so it has not really continued going down. It’s stayed stubbornly stable. The number of patients, the number of patients in hospitals, has actually ticked up a little bit. At UCSF the number of positive diagnoses ticked up in the last week.

We should feel very good about the last six weeks in the Bay Area, but there is a risk that we’re going to let down our guard and that things are going to get worse. There’s nothing about the virus that’s changed, and probably 99 percent of the people in the Bay Area are not immune to it. So the conditions for things to get bad are still in existence.

Why aren’t the numbers what you hoped?

In the places that got hammered, they’ve come down quite a bit, because when you get hammered everyone gets religion very quickly. In the places that haven’t — and we’re one of them — I think people are beginning to loosen up a little bit. And the virus is very predictably mathematic in its behavior. If someone has it — and we now know a lot of those people have no symptoms at all — they’re going to give it to on average three people, unless everybody is staying inside or 6 feet away.

I’m a little worried about the next phase. I think we’re at risk now to be overly optimistic and to say, “Look, it was far more benign than we feared, and we came nowhere near overwhelming hospitals and overwhelming ICUs. The number of deaths in the entire city of San Francisco has been 25. We can really relax and go back to something that too closely resembles our old lives.” I think that’s dangerous. And, yet, we can’t do this forever.

So it could be a cycle of easing restrictions and then getting stricter again?

You try something and we see what happens, and if it turns out things worsen, then you tighten things back up again. At some point you may even need to tighten them back up to April.

I think we do need to open up some. We need to do it gingerly and start with things that we think are very safe. Outdoor things are safer than indoor things. Things where people can predictably or reliably be 6 feet away or more are safer than not. And if everyone’s wearing a mask, they’re safer than not. So you begin with those things and then you take a breath and say, let’s watch for a week or two and see how it goes. And if it goes well we can open up a little bit more, and if it goes poorly we can close down.

What should policymakers be looking at to make evidence-based decisions about what happens next in the Bay Area?

It’s a really tough question, because it’s not irrational to be trying to balance the best possible things you could do for public health and the best possible things you could do for the economy and for people’s individual freedoms. Last month it was straightforward: The best thing we could do for both public health and the economy was to stomp down the virus to the extent that was humanly possible. In the next stage, I think if you’re a policymaker you have to be taking in multiple inputs … from public health experts and clinicians and hospitals, and inputs from business leaders and real people who are in many cases being devastated by this. The impact on the economy is palpable and quite horrible.

My prediction is that policymakers are going to be trying very hard to stick with a thoughtful, evidence-based, public health-oriented stand despite growing public and corporate pressure to loosen. That said, I think they will begin lightening or opening things up as the evidence becomes clearer that there are certain activities that are relatively safe. I think they will do this iteratively, as in little small experiments and then waiting a little bit and seeing what happens.

So, OK, you can go out to the golf course, you can go out to the beach and walk around. What do people do? Are they maintaining their distance? Are they wearing masks? And what is happening with case rates? That’s why detection is so important. If you just wait to see how many people get sick and come to the hospital and go to the ICU, you may be two to three weeks behind. We have to go and test some people to figure out what’s happening with new cases. You can’t just wait until they have a fever, and you certainly can’t wait until they’re sick enough to be in the hospital, because what you’re looking at then, it’s like looking at a star — you’re looking at two weeks ago, and it’s too late.

As an expert in your field, what has this time been like for you?

The world is evolving incredibly quickly. One of the things that’s been fun and challenging for people is to watch experts debate these things because the evidence is unfolding before our eyes. None of us knew anything about this prior to two months ago. This is all brand new, so we’re all kind of figuring this out as we go along. It evolves each day as the science evolves and new treatments come out.

If this wasn’t a terrible thing, it would be the most interesting thing I’d ever seen. It’s hard to get your head around the fact that it actually is both. It’s scary and horrible and just unbelievably interesting from every dimension of health care and science and public policy and the media and human behavior and culture.