What do epidemiologists think about Joe Biden and Mike Pence (and other national leaders) testing negative for COVID on Friday?

Testing and Contact Tracing

A: A negative test result does NOT mean that Mr. Pence and Mr. Biden are COVID-free… even if that happens to be really inconvenient for them.

Everyone who has been near the President of the United States in the last week (or who has been around anyone else with COVID-19 for that matter) should self-quarantine for 14 days following the last exposure. That means Joe Biden and Mike Pence should stay home.

This is the official guidance from the CDC, WHO, and leading institutions across medicine and public health. It’s not politics, it’s just science.

A negative test can arise from four different situations:

🆗 1. This person was not infected.

⏱️ 2. This person is infected, but it’s early in the course of their illness, so they don’t have much viral material to detect yet. They may go on to have a positive test later in the week.

🦠 3. This person is infected, but the sample just happened to not pick up any viral material, perhaps because it was done as a throat swab or it didn’t get far enough up their nose. Or just bad luck.

🧪 4. This person is infected and the swab did have viral material on it, but the test failed to return a positive result anyway due to a problem with the test itself or how the sample was handled.

Following exposure to the virus, we would expect some people to go on to have an infection and other people to escape infection. The reasons one person gets sick while another doesn’t aren’t totally clear at this point.

We can’t know in which group Joe Biden, Mike Pence, and others who were exposed to COVID-19 earlier this week will ultimately end up. Their negative test results could be because they aren’t infected (Situation 1 🆗 ), or could be false negatives (Situations 2-4 ⏱️🦠🧪 ).

And just in case it’s the latter, they should follow the guidance of the CDC and self-quarantine until they are certain they are not infected. Self-quarantine means stay home, do not have visitors, and do not put yourself in situations where you could give COVID-19 to other people. It does not mean go about your business with a mask on.

CDC Link

Johns Hopkins Link

WHO Link

Mayo Clinic Link

Let’s dive a little deeper into the sources of false negative test results.

⏱️ Situation 2: Test Was Too Early.

Whether a negative test is actually a “too early to tell” test varies according to how much time has elapsed since the person was exposed. When SARS-CoV-2 (the virus that causes COVID-19) enters your body, it starts invading cells, hijacking their machinery, and using it to make lots of copies of itself. Then those copies start shedding back out of our body in our snot and spit. This process takes a bit of time, and detecting the viral material depends upon the infection’s progress over the course of a few days.

The amount of viral shedding peaks right around when symptoms emerge, which can be anywhere from 2 to 14 days after exposure. The ability of a COVID test to pick up infection also varies along the same lines, although a test can detect an infection a bit before symptoms emerge (24-36 hours). Among those people who ultimately develop COVID-19 symptoms, just 5% of them will have symptoms within 3 days of the exposure. 50% will have symptoms within 5 days, and 97.5% will have symptoms within 12 days.

Basically, a negative COVID-19 test taken 3 days after a known exposure (such as at the Presidential debate) is just not very meaningful. At most, 2 out of 5 people who do go on to be symptomatic in the next couple of days would test positive at the 3 day mark. Annals of Internal Medicine COVID Incubation Period Article

Was the debate a “known exposure” for Biden? President Trump announced his positive test result 52 hours after the event ended on Tuesday night, and some outlets report that he appeared in poor health as early as Wednesday. We cannot rule out that President Trump was infectious at the time of the debate.

Other people at the debate were infectious. Trump’s advisor Hope Hicks, who was present at the debate, tested positive and was symptomatic on Wednesday, so she was definitely infectious at the debate. In addition, 11 members of the debate crew have since tested positive, as did the First Lady and Trump campaign manager Bill Stepien, who were also present.

Except for the fact that President Trump and Mr. Biden’s podiums were 12 feet apart and the audience was fairly sparse, everything at that debate was high risk for transmission: indoor space, prolonged duration, talking and shouting, and many people not wearing masks (including the candidates). Given the amount of shouting that occurred during the debate, aerosolization of particles seems possible, and 12 feet of space between the candidates may not have been sufficient. Also, we know little about what happened backstage. So yes, we think it qualifies as an exposure.
We’ll be waiting for the other shoe to drop through late next week. Slate Article on How the 6-Feet Rule Can Lead Us Astray

🦠Situation 3: Bad Sample.

Whether the test swab picked up viral material that was really present in the person’s body varies according to where and how the sample was taken. The two most common sample sites are the back of the throat and the nose or sinuses. Throat swabs are less accurate than nasal swabs, but even nasal swabs performed by trained healthcare providers return a negative test fairly often.
Nasal swabs are most accurate when they are taken from *way* up the nose and into the sinus cavities, which can be uncomfortable. The discomfort of the person being swabbed and the reluctance of some self-testers and even healthcare personnel to sample deep enough has led to questions around how depth of swabbing might affect test sensitivity, though these questions seem unresolved at this point. JAMA Article on Detection of SARS-CoV-2 in Different Types of Clinical Specimens

🧪 Situation 4: Bad Test Result Even Though There Was Viral Material Sampled.

Fundamental test accuracy varies depending on the type of test used and some luck. Sometimes the test’s chemicals don’t work right or the sample was handled incorrectly. And sometimes tests are inaccurate for unknown reasons.

There are two main types of tests, antigen tests and genetic tests (also commonly called PCR tests). Antigen tests return results quickly but have low sensitivity, which is another way of saying they return a lot of false negatives–as many as 1 in 2 negative results will be positive on a second test taken at the same time. PCR tests are more sensitive, but they still fail to detect the virus in as many as 1 in every 4 tests where a second test was positive. For the most part, we don’t know what type of tests were used for these high-profile leaders. Healthline Article: Fast Isn’t Always Better: What to Know About Rise of Rapid Coronavirus Testing

In short: Mr. Pence, Mr. Biden, and everyone else who was exposed to COVID-19 at the White House and campaign events this week: please stay home.

Our thoughts are with President Trump, First Lady Melania Trump, and everyone else who is involved in the tragic and preventable White House outbreak. We hope that you make a speedy and complete recovery.

Those Nerdy Girls at Dear Pandemic.

Our past posts on false negative PCR tests are here and here.

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