Here’s why a negative coronavirus test doesn’t necessarily mean you’re not infected

Marisa Iati,

The Washington Post

January 14, 2021 | 11:24 AM

Rampant neighborhood transmission of the coronavirus and a crippled vaccine rollout have boxed folks into a nook: Many are counting on negative test outcomes, inherently restricted in usefulness, as a certificates of clearance to see household and buddies.

While testing is vital to containing the outbreak, a negative test result’s not a free go to forgo social distancing, mask-wearing and huge gatherings. Here are a few reminders about what a negative coronavirus test means and doesn’t mean.

The exams nonetheless have various levels of accuracy

Coronavirus testing within the United States has ramped up considerably in latest months, with the each day test depend hovering round 1.5 million in January. There are two classes of exams: PCR (polymerase chain response) exams — thought-about the “gold standard” — and less-accurate antigen exams.

PCR exams use a molecular course of and are processed in a lab. Faster and cheaper antigen exams detect proteins on the virus’s floor. Most speedy residence exams, estimated to be about 90% correct, use the antigen expertise.

PCR exams are your greatest guess for getting a sense of whether or not you’re infected, despite the fact that these outcomes take longer than antigen outcomes. Still, PCR exams can lead to false negatives.

That’s partly as a result of the large cotton swabs utilized in lots of these exams could not choose up all traces of the virus deep in your nasal cavity. The virus could have moved out of your nostril to your lungs or elsewhere, or the swab could not have been inserted far sufficient.

But nasopharyngeal swabs, which acquire samples from the again of your nostril and throat, are nonetheless extra dependable than much less invasive throat swabs and nasal swabs.

A test could not be capable of detect the virus early in its course

Early in an an infection, the virus could not have reproduced sufficient to be detectable. The false negative charge of PCR exams on the day of publicity is 100%, however falls to about 38% 5 days later as signs often set in, in keeping with an evaluation printed within the Annals of Internal Medicine. The charge decreases additional, to about 20%, after three extra days.

“We don’t yet understand exactly when a person who’s infected will start testing positive for the virus,” Muge Cevik, a medical lecturer in infectious ailments and medical virology on the University of St. Andrews, advised The Washington Post in December. “So there are situations when a person could test negative, but they could still be contagious.”

If you suppose you’ve been uncovered to the coronavirus however obtain a negative test consequence, you might wish to get examined once more in a few days. You also needs to self-quarantine whereas you’re ready for outcomes.

The Centers for Disease Control and Prevention suggests quarantining for 14 days however considers 10 days acceptable for those who haven’t skilled signs. The company additionally says it’s most likely protected to depart your house after seven days you probably have no signs and have obtained a negative test consequence.

You may test negative and turn into infected quickly afterward

On high of the opposite limitations, a coronavirus test captures only one second in time. You may stroll out of a testing middle and instantly contract the virus. The test you simply took is not going to mirror your new an infection.

This constraint is especially vital to remember for those who plan to journey after you be taught the result of your test. A crowded airport terminal or rest-stop restroom may expose you to the virus after you’ve concluded that a negative test means you’re not infected.

Gathering indoors is inherently dangerous, and a negative test consequence doesn’t inform the total story.

The Washington Post’s Natalie B. Compton, Melody Schreiber and William Wan contributed to this report.


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