A negative test does not guarantee that you do not have COVID-19: how to know for sure

If you think a negative test result means that you do not have coronavirus, you may be wrong. CNN.

Photo: Shutterstock

It may take several days for an infection to show up in a Covid-19 test.

“We know that the incubation period for Covid-19 is up to 14 days. Until then, you can test negative and not have any symptoms,” emergency medicine physician Dr. Leana Wen told CNN. “But you can be a carrier of the virus and transmit it to others.”

So, if you want to get tested as a precaution before seeing your friends or family, here's what you need to know.

If you got infected yesterday, will today's test confirm this?

Probably no. A study published in the medical journal Annals of Internal Medicine looked at false negative test results in people who did have Covid-19. Within four days of infection, before symptoms usually showed up, there was a 100% chance of getting an incorrect / negative test result.

The day people started showing symptoms, the study found, the average false-negative rate dropped to 38%. Three days after the onset of symptoms, the false negative rate dropped to 20%.

“The virus simply needs time to replicate in the body to detectable levels,” said Justin Lessler, senior author of the study and assistant professor of epidemiology at the Johns Hopkins University School of Public Health. “You may become infected with just a few viral particles, but they will not be detected until they have had time to replicate to adequate levels for detection.”

How long does it take to get tested after a possible infection?

“There is no hard and fast rule, but the evidence suggests that getting tested before the third day after exposure makes little sense,” Lessler said.

Can you be contagious if the test is negative?

Yes.

“People think that if you test negative, you are safe. Actually, no,” said Dr. Rochelle Walensky, chief of infectious diseases at Massachusetts General Hospital.

People who get Covid-19 can show symptoms within two weeks, but on average, it happens after five days, Walenski said.

"It's generally thought that you're most contagious two days before and two days after," she said.

One of the reasons the virus spreads so easily is because people can get infected from those without symptoms. The US Centers for Disease Control and Prevention estimates that 40% of infections are asymptomatic and 50% of transmissions occur before symptoms appear.

“This is one of the biggest vulnerabilities. And one of the biggest problems and surprises is because this is not the case with other “relatives” of the coronavirus, Walensky said. “The reason we were able to control the SARS outbreak so quickly—even though there were a lot of deaths—but it didn't become a pandemic is because people didn't shed (the virus) until they had symptoms.”

Do different types of Covid-19 tests matter?

When it comes to diagnostic tests—those that determine whether you have an active coronavirus infection—there are two main types:

Molecular tests such as PCR testslooking for the genetic material of the virus. Most of these tests are done with nasal or throat swabs, although some can be done using saliva, according to the US Food and Drug Administration.

“This test is generally very accurate and usually does not require repeating,” the FDA says.

On the subject: 'Nightmare side effects': a volunteer on the Russian vaccine against COVID-19

But the downside to molecular testing is that it can take a while to get results, anywhere from a few hours to a week after testing.

“For people who show symptoms, research so far shows that the accuracy of a molecular test to detect a positive result increases every day after infection,” said Pia McDonald, an infectious disease epidemiologist at the nonprofit research institute RTI International.

But for infected people who are asymptomatic, the accuracy rates are less obvious.

“Research on the effectiveness of molecular tests in asymptomatic people is very limited,” she added.

Antigen tests, often called "rapid tests" (although some molecular tests are also fast). Antigen tests are not antibody tests, which tell you whether antibodies have been produced against an infection.

Antigen tests do not look for the genetic material of the virus, unlike molecular tests. Instead, they look for specific proteins on the surface of the virus.

The good news is that you can get your antigen test results in less than an hour. The bad news is that you are more likely to get a false negative result.

“Positive results are usually very accurate, but negative results may need to be confirmed with a molecular test,” the FDA says. “Angen tests are more likely to miss active coronavirus infection than molecular tests.”

This may help explain some of the more recent White House-related Covid-19 cases. White House officials often use rapid antigen tests, which tend to have a higher false-negative rate than molecular tests.

No matter what type of diagnostic test you use, you are usually more likely to get a false negative than a false positive.

“If the molecular test is positive, it is an accurate reflection of infection,” McDonald said. — If the result is negative, then the reliability is lower. It’s the same with antigen tests.”

Can the test be done at home?

Yes. There are several home testing kits available, such as the Everlywell Covid-19 molecular test. People take samples of nasal swabs and mail them to the laboratory, which sends the results digitally within 24 to 48 hours after receiving the samples.

But taking any Covid-19 test too early could miss the infection, said Dr. Frank Ong, chief medical officer and research scientist at Everlywell.

“My best advice is to treat yourself as if you are likely infected after likely exposure. Go into quarantine, wear a mask that covers your nose and mouth, and practice good hygiene. If you want to take extra precautions or think you may have been exposed, get tested for the virus using an FDA-approved Covid-19 test.”

What if you want to see friends or family?

If you insist on seeing your loved ones for Thanksgiving, Walenski said, a 14-day quarantine would probably be your safest choice.

“If you do it right, you won't need a test,” she said. “Probably the cleanest way to do it.”

To be clear, quarantine means staying at home. This does not mean that you can run for business.

“Grocery shopping and quarantine don’t mix,” Walensky said.

“Adding testing to your list of precautions is helpful, but only if done correctly,” she said. “And if you don’t know exactly when and how to use it, then you may well be lulling yourself into a false sense of security.”

Loessler agreed that quarantine is best and testing should be done wisely.

“If you are visiting an elderly family member and have a reasonable risk of exposure, there is no substitute for 14 days of quarantine,” Lessler said.

“At least I would wait 10 days and get a negative result. If you are visiting a younger, healthier family member and you have little chance of being infected before or during your trip, then 5 or 7 days (quarantine) plus a negative test is likely to significantly reduce the risk, although it does not guarantee safety. In any case, you should stay in quarantine, awaiting test results, and make sure everyone you plan to meet is familiar with the contamination risk control plan.

On the subject: Russian virologist infected himself with COVID-19 twice: why does he need it

There have already been cases of coronavirus spreading in families just days after testing negative, according to Michael St. Louis, a member of the CDC Community Leadership Group. He said that everyone should remember to treat family members living separately the same way they would treat friends or colleagues.

Of course, the best way to ensure the safety of all your loved ones is to celebrate the holidays remotely.

“I have three children... And my parents are not going to join us this year,” Walensky said. - That's just terrible. But in reality, I will never forgive myself if I harm my parents. I'm just looking forward to 2021 when we can be together."

CDC offers to celebrate with loved ones virtually online. You can also prepare traditional Thanksgiving meals and deliver them without contact to relatives, neighbors, or anyone who might feel lonely.

Walenski said the small sacrifices made this Thanksgiving will help ensure everyone is healthy enough to sit down to the table next year.

“At least they will be alive and well next year, whereas irresponsible behavior now could mean someone is no longer at the holiday table,” she said. “Let’s do this so that we have a much better chance of meeting each other healthy in 2021.”

Read also on ForumDaily:

Coronavirus mutations: is it true that strains of SARS-CoV-2 are becoming more dangerous

Sweden did not introduce quarantine: how it affected the development of the COVID-19 pandemic

Card, money and smartphone: coronavirus can live on some surfaces for up to 4 weeks

The CDC officially recognized another way of spreading coronavirus

Do you want more important and interesting news about life in the USA and immigration to America? — support us donate! Also subscribe to our page Facebook. Select the “Priority in display” option and read us first. Also, don't forget to subscribe to our РєР ° РЅР ° Р »РІ Telegram  and Instagram- there is a lot of interesting things there. And join thousands of readers ForumDaily New York — there you will find a lot of interesting and positive information about life in the metropolis.