An indoor gathering at the White House with President Donald Trump in attendance

Before announcing judge Amy Coney Barrett (far right) as his Supreme Court nominee during a ceremony on 26 September, US President Donald Trump (left) mingled with attendees at the White House.Credit: Doug Mills/The New York Times/Redux/eyevine

US President Donald Trump is reportedly doing well after a brief stint in hospital following a COVID-19 diagnosis, but questions remain about how he contracted the coronavirus and whether he infected others.

It is widely thought that a ceremony at the White House on 26 September, to announce judge Amy Coney Barrett as the president’s pick for an empty seat on the Supreme Court, could have been ground zero for a cluster of infections. Ten days later, more than a dozen people who travelled with the president or attended events with him, including White House staff, journalists and elected representatives, have disclosed positive tests. Trump’s presidential debate with Joe Biden in Cleveland, Ohio, meanwhile, has been linked to at least 11 cases of COVID-19. (Biden has since tested negative for the coronavirus.)

Despite these events and others that might have created opportunities for the virus to spread, the White House said on 5 October that it would not be divulging how many of its staff members have tested positive for SARS-CoV-2. Also, the administration will reportedly not be ‘contact tracing’ the White House ceremony, meaning it will not be studying attendees’ movements and then notifying people they were in contact with to quarantine and thereby prevent further viral spread.

Nature asked Emily Wroe, a physician and one of the leaders of the contact-tracing team Partners In Health, a Boston-based non-profit organization which has been assisting health officials in Massachusetts, whether the cases linked to the White House constitute a ‘superspreader’ event, and what an effort to trace them would look like.

Was the White House ceremony a ‘superspreader’ event?

It’s definitely a cluster [an event that is a source for multiple infections]. That seems logical — we don’t think that everybody walked in with the coronavirus. What we know about COVID-19 is that it doesn’t spread symmetrically. So if you see a bunch of people with COVID-19, some of them might give it to zero people or one other person. And then there might be an event or a case where a lot of people get it.

Was the ceremony ideal for spreading the virus?

The virus doesn’t care if you’re a college student or a politician or in a backyard barbecue at your kid’s friend’s house. We’re all good hosts. Based on what we know about how COVID likes to spread — indoor spaces, close conversations with people over a prolonged period, crowded places — parties and events are excellent for the virus.

Portrait of Emily Wroe

Emily Wroe is co-leader of a contact-tracing team at Partners in Health, a non-profit body based in Boston, Massachusetts.Credit: Cecille Joan Avila

How would you approach contact tracing under those conditions?

First, we make sure that all of the cases and all of the contacts are identified. Everybody with COVID needs to be interviewed: did you eat anywhere else, did you shop for anything, did you buy anything, did you go to any routine meetings? Then all of those contacts that get identified get a phone call. We let them know they were exposed, and then make sure that they get tested, and that they get into quarantine for two weeks after their exposure date, regardless of the test results [because sometimes tests can give false negatives].

Trump travelled to at least seven US states within a week of his diagnosis. What would the logistics of tracing that look like?

Most of our interviews with a case will take maybe a little over an hour. It would be a massive effort for case investigators to get a list of all of the contacts who’ve been exposed. [In the case of the President’s movements], it really would be a collaboration state to state — between the public-health departments — to make sure that all of our contacts are notified about their exposure, testing is arranged, and they’re told and educated about quarantining for two weeks. It’s massive but it’s very feasible. It’s a core public-health tool and one that we know works.

Why is it important to do this quickly?

The point of contact tracing is to find all the people who might get the virus and protect them from spreading it further. And that timing is really important because we can’t just wait until people might get symptoms, might get a test — and then wait until the next day for their test results.

It’s been reported that the White House is not doing contact tracing. What are the implications?

It’s a missed opportunity to prevent additional spread.

The White House has declined to reveal how many of its staff members are infected, citing privacy concerns. Does contact tracing violate privacy?

It’s important that we draw public lessons from what we’re learning. So you might see states say, “We are seeing clusters in restaurants, and this is how many cases and contacts it’s led to.” But you don’t see them saying “these people at this restaurant”. It’s presented in a way that’s not calling out specific individuals who may or may not have COVID. But overall rates of positive testing and that sort of thing are quite common things that we see shared.

We really work hard to protect people, which can be important in times when COVID is threatening employment — for example, with small businesses. So we’re very careful not to reveal identity unless we have that permission. What gets shared, I think, needs to inform public information, so that people are educated and feel safe and have the information that they need.

What’s one unknown about the virus that makes contact tracing hard?

One thing we wonder about is, how do we predict which cases will be most infectious? I don't think we have the recipe or the algorithm to [work out] what exactly leads to that. It’s not as simple as the more symptoms somebody has, the more infectious they are. We don't have objective measurements to predict, out of five patients, which of them might be the one at a party that spreads it to a lot of other people.