If Trump's symptoms started before Friday, he may have been highly infectious during the debate
- President Trump tested positive for the coronavirus on Friday.
- People who have COVID-19 are generally most infectious the day they start showing symptoms and the day prior.
- So if Trump started showing symptoms before Friday, that means he might have been highly infectious when he debated Joe Biden on Tuesday.
- Biden tested negative on Friday, but experts say he should be re-tested frequently since the coronavirus' average incubation period is five days and could be longer.
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President Donald Trump's announcement that he'd tested positive for the coronavirus raised an immediate question among health experts, the public, and members of Joe Biden's campaign: When did his symptoms start?
"The highest infectious period — the period at which you're spewing the most virus — is your onset of symptoms and possibly the day before," Monica Gandhi, an infectious-disease expert at the University of California, San Francisco, told Business Insider. She added, "it really is at that point where you're shedding more virus from nose and mouth that can be given to other people."
Trump tweeted about his diagnosis early Friday morning. Earlier this week, he debated former Vice President Joe Biden on Tuesday; attended a private fundraiser and a 3,000-person rally in Duluth, Minnesota, on Wednesday; then met around 100 people for another fundraiser in Bedminster, New Jersey on Thursday.
All those contacts are at risk, experts say, but knowing the more precise timeline of Trump's infection would reveal who among them was near him when the president was at his most infectious.
"It's a lot of exposure here. This is a contact tracing nightmare," Gandhi said.
Bloomberg News reported that a few aides think Trump might have been exhibiting symptoms on Wednesday. If that's true, it would mean Trump may have taken the debate stage at the time when he had the highest chances of transmitting the virus to Biden.
Biden and his wife, Jill, tested negative for the coronavirus on Friday. But the virus' average incubation period — the time between when a person gets infected and when they start showing symptoms or test positive — is four or five days.
So if Biden was exposed at the debate, he may not get a positive test result or experience symptoms until Saturday or Sunday.
When viral load is highest
A person's infectiousness is linked to their viral load: how many viral particles they're carrying and shedding into their environment.
"It's usually around the time right before the symptom onset and around the very first days of symptoms is when the viral load is generally the highest," Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security, told Business Insider.
Mandel Ngan/AFP via Getty Images
Indeed, several studies have shown that COVID-19 patients can easily spread the virus before they know they're sick — that's known as pre-symptomatic transmission.
Based on that research, Adalja said, Trump was infectious "probably about a day before symptoms started."
Trump's campaign sent all attendees of the Thursday New Jersey fundraiser an email on Friday urging them to contact a medical provider if they develop COVID-19 symptoms.
Experts say Biden needs to get tested again and should not be campaigning
Olivier Douliery-Pool/Getty Images
If Trump was infectious at the debate, the setting may have been ideal for the virus to spread.
Although Biden and Trump stood about 10 feet apart onstage, the event was held inside, neither man wore a mask, and both spoke vigorously. Studies have shown that talking loudly and forcefully exhaling can lead a person to spew viral droplets and aerosols farther than 6 feet. Transmission is also more likely in poorly ventilated indoor spaces.
Given that, Gandhi said, it's reasonable to worry about Biden's exposure.
"There were no masks. It was indoors. And the concerning part is that Trump yelled straight for 90 minutes," she said. "And the louder volume, the constant talking can be kind of like singing. It's loud — it's a forceful exhalation."
Spencer Platt/Getty Images
Guidance from the Centers for Disease Control and Prevention recommend a 14-day quarantine for anyone with known exposure, since that's the maximum amount of time it takes for the coronavirus to incubate.
The Minneapolis Department of Health recommends that people get tested five to seven days after an event where they might have been exposed. A test before that point isn't considered reliable, since an infection might not show up right away. Even if that first test comes back negative, the Minneapolis department adds, people should get tested again at the 12-day mark.
That likely applies to Biden, even though he and Trump weren't standing within 6 feet of one another. However, the former vice president announced after his negative test that he'd resume cross-country campaigning.
"You can't test yourself out of self quarantine," Gandhi said, adding that Biden "shouldn't be campaigning."
Morgan McFall-Johnsen contributed reporting to this story.
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