US president Donald J. Trump and his wife Melania tested positive for Covid-19 late on Oct. 1 after a full week of presidential debating and campaign rallying. He tweeted the result early on the morning of Oct. 2.
Since then, two White House correspondents have also tested positive for the virus, as well as a few people who attended the Supreme Court nomination for Judge Amy Coney Barrett held on Sept. 26. While a subject of much debate is where these cases may have originated and if they’re connected, there’s also critical work going on to contain the spread from the known infections—before future cases balloon out of control.
For that, we need contact tracing. As you read this, Trump’s immediate contacts are being identified and contacted. Those who got close to Trump after he was infected will need to go into quarantine, defined as a 14-day period of having no contact with anyone, regardless of whether they develop symptoms.
It sounds straightforward in theory—but in practice, it’s a lot harder. When we talk about contact tracing for Trump’s potential Covid-19 exposure, what we really mean is identifying the people who’ve been exposed to Trump in a handful of specific ways, between the time that he encountered the virus and the time that he tested positive. And that’s where things get a little messy.
When did infection happen?
It’s hard to pin down when someone was initially infected with Covid-19 because of the nature of how SARS-CoV-2 enters the body: slowly, one cellular ACE2 receptor at a time, which can trick individuals into thinking they’re healthy even after they’ve been infected.
On average, “you have two days of incubation, in which a PCR test wouldn’t test the virus,” says Brooke Nichols, a health economist at Boston University who uses mathematical models to map infectious spread. During these two days, a person likely wouldn’t have enough of a viral load to infect others.
Then, however, most people enter a pre-symptomatic phase. This is the danger zone: A person is sick, still not showing symptoms, but has enough of a viral load to potentially infect others. This when people are most likely to give the virus to others. Once a person does have symptoms, they’re (usually) wise enough to get tested, tell others, and isolate.
Based on what we know about the appearance of Trump’s symptoms and the test he took on Oct. 1 that came back positive, he could have been exposed, infected, and contagious to others as early as the beginning of the week.
Who counts as a contact?
Trump had a busy week before getting his test results. Between multiple rallies and a presidential debate with Joe Biden, he likely saw thousands of people—not just his immediate staff.
The good news is, even if Trump was infectious the entire week before his positive test, it’s unlikely that he infected everyone he was around, says Emily Gurley, an epidemiologist at Johns Hopkins University who created a course on contact tracing.
In epidemiology, a contact has specific definitions. The US Centers for Disease Control and Prevention identifies two main categories: First, there are those who have experienced physical touch with a person who tests positive. “That’s pretty easy to define, you shake hands, hug—whatever,” says Gurley.
Then, there are those who come with six feet (two meters) of an infected person for more than 15 minutes. In this case, that’d mean people that have had an in-person meeting with the president for longer than 15 minutes. People who were merely at a campaign rally in front of Trump would not be considered some of his immediate contacts, unless he stopped to shake their hand.
With the exception of healthcare professionals wearing medical grade N95 masks, whether an individual contact was wearing a mask doesn’t really matter to a contact tracer, Gurley says. This is because there’s no way to verify what kind of a mask that person was wearing, and whether they were doing so correctly. So even if a person was wearing a mask while closely talking to someone who tests positive for Covid-19 later, the person wearing a mask should still quarantine.
Gurley has a third category she likes to think about, called proximate contacts. These are individuals who are more than six feet apart, but have been sharing an indoor space with someone who is infected for two or more hours. Epidemiologists have seen this kind of transmission in the cases of choir practice or indoor dance practices.
Would that mean that Democratic candidate Joe Biden counts as a contact, after debating Trump on Sept. 29? It’s impossible to say for sure—their podiums at the debate were placed 12 feet and eight inches apart (more than three meters). But this certainly enters a gray area.
Should close contacts of someone with Covid-19 get tested?
Biden, vice president Mike Pence, and their respective spouses have all received negative Covid-19 tests in light of the news that Trump and the first lady have tested positive.
But that’s probably not enough to say that they don’t have Covid-19, says Gurley. “Tests help tell you when you’re infectious,” she says. If you do test positive, you’d want to isolate and begin tracking down your own contacts.
However, it’s unwise to take a negative test result to heart if you know you have been exposed to Covid-19. If you took the test too early, it’s possible that the virus didn’t have enough time to replicate within your system for the test to register its presence.
That’s why even those who don’t have symptoms but are known contacts of a positive Covid-19 case should still quarantine themselves for 14 days, Gurley says. This way, there’s no chance that they could infect others, even if they have an asymptomatic or only mildly symptomatic case.
Biden is still traveling as part of his presidential campaign at the time of writing, although he has scaled down his schedule to just one event. Pence is not quarantining, because, per his physician, he doesn’t meet the criteria for being a close contact (he was not with Trump after Sept. 28).
Who gave Trump Covid-19? Does it matter?
At the moment, no one knows—though hours before Trump announced he had Covid-19 on Twitter, Bloomberg reported that one of his senior aides, Hope Hicks, tested positive. On Sept. 29 Hicks had been aboard Air Force one with Trump and others as he traveled to the debate in Cleveland, and then to Minnesota for a campaign rally. She reportedly felt sick in Minnesota, so isolated herself on the plane ride home.
That means Hicks could have given Trump Covid-19. But given that they tested positive around the same time, it’s possible that one person exposed both of them, says Gurley. And that possibility introduces the need for a totally different approach to contact tracing—not just in the White House, but in general.
Identifying, quarantining, and potentially testing every one of Trump’s contacts in the last week, when it was likely he was exposed—the traditional contact tracing approach—would successfully squash any outbreaks that stem from him, alone. But it wouldn’t stop any outbreaks that started with the person who infected Trump.
A different approach would attempt to identify the missing link between a growing number of positive cases connected to the White House. If we could trace all of their contacts backwards in time, we could potentially identify an infected person who exposed them all.
This is not a matter of assigning blame. As Zeynep Tufecki explains in the Atlantic, tracing all the contacts of that earlier infection node could increase the likelihood of catching more cases before they infect others.
If there were hard and fast rules to disease spread, managing the whole pandemic would have been a heck of a lot easier. Unfortunately, biology is more like the English language: It follows rules sometimes, but has a tendency to be unpredictable. That’s why it’s paramount to err on the side of caution when disease could spread. Currently, the White House hasn’t changed any of its safety procedures in light of president Trump’s positive test, aside from moving campaign events virtual.