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A 15-minute COVID test?

MIT Medical answers your COVID-19 questions. Got a question about COVID-19? Send it to us at CovidQ@mit.edu, and we’ll do our best to provide an answer.

Our adult son is moving back home. My wife and I are at higher risk for complications of the virus, so we’ve been self-isolating, and we’d like our son to have a COVID test before moving in with us. We called a local urgent care facility, and they offered us a 15-minute test. Is this a reliable test? If not, what other tests should we consider?

Illustration of a gloved hand placing sample cartridge into an antigen testing device with a display indicating: results in 15:00

The test in question would be an antigen test. It’s like a rapid strep test, but for COVID-19. And, just as a rapid strep test can sometimes provide a quick diagnosis for a kid who shows up in the pediatrician’s office with a sore throat and fever, the COVID- 19 antigen test can be a good first step in diagnosing a patient who presents with symptoms of COVID-19.

But even in people who have symptoms of coronavirus, the antigen test often fails to identify people who are actually infected with SARS-CoV-2, the virus that causes COVID-19. Just as your doctor may order a throat culture to definitively rule out strep throat when a rapid strep test comes back negative, the FDA recommends using the more sensitive COVID-19 PCR test for symptomatic individuals who test negative. And for an asymptomatic individual like your son, the antigen test would be fairly useless.

The PCR test, which looks for genetic material from the virus, requires expensive and specialized equipment. It can take many hours or days to get results. But at this point in time, it is the only appropriate screening tool for use with asymptomatic individuals.

On the other hand, should you add someone to your household — or “bubble” — based on a single negative PCR test?

We’d say no. Since the incubation period for the virus can be as long as 14 days, a negative test does not definitively rule out exposure or infection. All it tells you is that an individual’s sample did not show viral levels high enough to be reliably measured at that particular moment in time.

For that reason, the process of merging households should involve some period of self-quarantine for your son — either before or after he moves in. It’s terribly inconvenient and difficult to live with someone who is self-quarantining, but it can be done. There are two options:

  • A 14-day self-quarantine period, or
  • A negative COVID-19 PCR test, followed by seven days of self-quarantine, followed by a second negative PCR test.

Successfully completing either option should reassure everyone that your son is not infected, and you could safely “merge your bubbles.” Of course, adding another person to your household bubble increases your risk going forward, so be sure to have a frank discussion about the ground rules that everyone in the household will agree to follow with regard to precautions — something that’s even more important since you and your wife are at higher risk of complications from the COVID-19 illness. While this discussion may be awkward, making sure you’re all on the same page now avoids even more awkwardness later on and will help to assure that you all stay safe and healthy as a household of three.

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