Contact Tracing the President

How did he get the virus, and who else might he have infected? Let the detective work begin.

President Donald Trump speaks at a “Make America Great Again” campaign rally at Duluth International Airport in Duluth, Minnesota, on September 30. Credit: MANDEL NGAN / Getty Images

It was the tweet heard ‘round the world: President Donald Trump and first lady Melania Trump tested positive for Covid-19. Only a few hours later, there is rampant speculation about the timeline and source of the president’s infection. How did he contract the virus, and who else might he have infected? Two epidemiologists shared with Elemental how they approach this question from a contact tracing perspective. Let the detective work begin.

When was Trump exposed to the virus?

The current assumption is that after a person gets infected with the novel coronavirus, it takes at least 48 hours to produce enough viral particles to both be contagious and to test positive. It can take another two days before the immune system kicks in and the infected person develops symptoms. However, both of these time frames can be extended, either because it takes more time for the virus to replicate, and/or because the immune system needs more time to ramp up.

“50% of people who are exposed and will go on to get symptoms get them by day five, which means that they could potentially have tested positive as early as day three [post-infection],” says Eleanor Murray, ScD, an assistant professor of epidemiology at Boston University. “97% have developed symptoms by day eleven.”

With a first positive test on Thursday and the onset of mild symptoms on Friday, Trump was likely exposed to the virus either late last week or early this week.

“The situation at the White House is different from what it would be for the general public. Because they’re doing daily testing, you can really identify the 24-hour window when somebody was likely infectious to others or not.”

How did the president get infected?

One theory is that he got the virus from White House aide Hope Hicks, who tested positive on either Wednesday evening or Thursday morning (accounts are conflicting). Notably, Hicks tested negative for the virus Wednesday morning (White House staffers are tested daily). She then accompanied the President on an Air Force One flight to Minnesota for a rally and fundraiser with GOP state leaders. After reports that she wasn’t feeling well that afternoon, she tested positive on a second test.

Celine Gounder, MD, an infectious diseases specialist at NYU Langone, says that if a person has a negative test, in all likelihood they are not infectious. “The PCR test that they’re using is very sensitive, and so if you’re not positive on the test, it’s very unlikely you have enough virus around to transmit to other people,” she says.

That would mean Hicks likely didn’t infect the president earlier in the week because if she was shedding too little virus to test positive, she was also shedding too little virus to infect someone else. However, it is possible that her viral load was low enough to not be caught by the test Wednesday morning but then ramped up during the course of the day, making her infectious in time for the flight home on Air Force One with the president that afternoon (reports say she quarantined on the flight back to Washington, though it’s unclear what that involved).

Even more confusing is the fact that Hicks tested negative and developed symptoms on the same day (Wednesday), which is unusual. Remember, people typically have enough virus in their body to test positive and infect others a few days before they are symptomatic. Murray says it’s “solidly within the realm of possibility” that Hicks’ test Wednesday morning was actually a false negative and she could have been infectious earlier. Reasons for a potential false-negative result include a bad swab that didn’t pick up all the viral particles in the nose or even just a faulty test.

Here’s another possible scenario: Hicks could have been infected at the same time as Donald and Melania Trump, potentially during the Supreme Court nomination ceremony on Saturday. It’s emerged that (as of press time) two other attendees that day — Utah Senator Mike Lee and University of Notre Dame President Rev. John Jenkins — also recently tested positive for the virus. While the event was held outdoors in the White House Rose Garden, several hundred people were in attendance, few wore masks, and distancing was nonexistent.

Another person infected on a similar timeline as the president is Republican National Committee Chair Ronna McDaniel. She tested positive for the virus on Wednesday and had met with the president at a fundraiser the previous Friday, just five days earlier. It’s unclear if McDaniel was also receiving daily tests, so she might have been asymptomatically infected with the virus at their meeting but still been shedding enough viral particles to expose Trump.

We may never know the true route of exposure. This type of detective work — called retrospective contact tracing — is tricky because it can take anywhere from two to 14 days from exposure to the virus to have a positive test, Murray says. “If he just [tested] positive yesterday, probably that means an infection happened relatively recently… But it’s also possible that he could have been exposed as long as two weeks ago, and it could have taken that long for the infection to take hold,” she says.

Did the President infect others?

An easier — and in many ways more important — form of contact tracing is to stop the chain of transmission going forward.

Scientists think that people are most infectious during the two days before they develop symptoms, plus on their first symptomatic day. In Trump’s case, that means he could have been shedding a high enough quantity of virus to infect another person as early as Tuesday or Wednesday. In a normal situation, a contact tracer would work 48 hours backward from the first positive test and recommend everyone who had close contact with the infected person during that time quarantine for two weeks. That would include everyone who was at the presidential debates on Tuesday. However, because the White House is conducting daily tests, Gounder says the potential window of contagion narrows to just the 24 hours between tests.

“The situation at the White House is different from what it would be for the general public,” she says. “Because they’re doing daily testing, you can really identify the 24-hour window when somebody was likely infectious to others or not.”

If Trump tested negative on Wednesday, only those who had contact with him between that negative test and his positive test on Thursday would need to quarantine. This is likely a relief to the Biden campaign following the debate on Tuesday, but less good news for the GOP reps and donors Trump met with on Wednesday and Thursday, who now have to quarantine for 14 days.

What about all the people, such as Vice President Mike Pence, who’ve had recent contact with the president but tested negative for the virus today? Unfortunately, Gounder says, they’re not out of the woods yet.

“Just because you have a negative test result today does not mean that you will remain negative. For example, the vice president has tested negative so far, but it can take up to 14 days from the time of exposure for a test to turn positive or to develop symptoms,” she says. “This is why you still need to quarantine for 14 days after the exposure even if you have a negative test because you could still turn positive on day two, three, four, five out to 14.”

Murray and Gounder say that this scenario exemplifies why daily testing is useful and important, but not a guarantee against infection. The daily tests can catch a case very quickly and prevent a person from spreading the virus further. However, there is always a window between the two tests when someone could turn from negative to positive and be spreading the virus. That’s why it’s essential to combine testing with other safety measures like social distancing and mask-wearing, just in case.

Health and science writer • PhD in 🧠 • Words in Scientific American, STAT, The Atlantic, The Guardian • Award-winning Covid-19 coverage for Elemental

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