In the run-up to Thanksgiving, Americans are no stranger to planning. But this year, as they prepare to thaw turkey brine and pie crusts, people across the country are waiting for something special: a coronavirus test they hope will make them mingle with loved ones.
Many people consider a negative coronavirus test a ticket to socializing freely without taking precautionary measures. However, scientists and doctors say this is dangerously wrong. This is a precautionary measure but does not negate the need for others, such as quarantine, masking, and distancing.
The main reason is that a test at some point will provide information about the extent of the virus. A person might be infected but not yet have enough viruses to register for a test. Or a person can become infected in the hours or days after a test is performed. In addition, the tests are not 100 percent accurate.
"Requiring all of your guests to email you a negative test result before your Thanksgiving dinner will definitely reduce the risk of an outbreak – but not entirely," said Dr. KJ Seung, Head of Strategy and Policies for the Covid Response at Partners in Health. However, this is a common misperception that contact tracers hear when talking to people, he said.
The experts agreed that tests are very useful for one thing: if someone gets a positive test, that person knows they need to stay home and isolate. A negative test, while helpful, is not enough, said Dr. Esther Choo, Emergency Medicine Physician and Professor at Oregon Health and Science University.
A test "filters out those who are positive and definitely shouldn't be there," she said. “Testing negative basically doesn't change the behavior. It still means wearing a mask, keeping your distance, and avoiding indoors when you can. "
Not all tests are created equal
Different tests for the coronavirus give different information.
Laboratory tests based on a technique known as the polymerase chain reaction or P.C.R. can detect the virus if it is already present in very small quantities. However, it can take a few days for results to return, giving someone time to show themselves. Antigen testing is faster, cheaper, and more convenient – it can give you results in minutes – but they're also more likely to miss out on the virus when it's scarce. To obtain emergency clearance from the Food and Drug Administration, antigen testing for the coronavirus only needs 80 percent of the P.C.R. Many rapid tests are also not approved for use on people with no symptoms.
In some cases, a person who tests negative with an antigen test can be told by P.C.R. – Increase the risk that a negative antigen test will make someone feel false on the way to Thanksgiving dinner, said Paige Larkin, a clinical microbiologist at NorthShore University HealthSystem in Chicago, where she specializes in diagnosing infectious diseases.
Why tests alone are not enough
"A negative result is a snapshot," said Dr. Larkin. "It tells you that the exact second you are tested, the virus went undetected. That doesn't mean you aren't infected."
After infiltrating a person's body, it can take several days for the virus to build up. In the meantime, there may not be enough virus for a test to detect it. But the person could still be infected or contagious in the meantime. A person who tests negative one day may turn positive just a day later, or even an hour later. People can spread the virus in the days before they first feel sick and can spread the virus even if they never develop symptoms.
"The challenge for the individual, then, is that testing negative today doesn't mean a person will be negative tomorrow or the day after," said Natalie Dean, assistant professor of biostatistics at the University of Florida.
If you do multiple tests over a period of days, you will get a clearer answer. However, experts warned that no test – regardless of how often it is done in succession – can definitely determine whether someone infected with the coronavirus is contagious or no longer poses a risk of transmission to other people.
The October White House outbreak is a good example of what can happen when a group of people relies heavily on testing and ignores other strategies to limit the spread of the virus.
In an informal poll of 670 epidemiologists, only 6 percent said that if they recently tested negative for the virus, they could spend time indoors without taking precautions. 29 percent said they would if everyone also used masks and stayed away. And 64 percent said that even if they tested negative, they wouldn't like to hang out with people they don't live with.
The coronavirus outbreak>
Things to know about testing
Confused by Coronavirus Testing Conditions? Let us help:
- antibody: A protein produced by the immune system that can recognize and attach to certain types of viruses, bacteria or other invaders.
- Antibody test / serology test: A test that detects antibodies specific to the coronavirus. About a week after the coronavirus infects the body, antibodies start appearing in the blood. Because antibodies take so long to develop, an antibody test cannot reliably diagnose an ongoing infection. However, it can identify people who have been exposed to the coronavirus in the past.
- Antigen test: This test detects parts of coronavirus proteins called antigens. Antigen tests are quick and only take five minutes. However, they are less accurate than tests that detect genetic material from the virus.
- Coronavirus: Any virus that belongs to the Orthocoronavirinae virus family. The coronavirus that causes Covid-19 is known as SARS-CoV-2.
- Covid19: The disease caused by the new coronavirus. The name stands for Coronavirus Disease 2019.
- Isolation and quarantine: Isolation is separating people who know they have a contagious disease from those who are not sick. Quarantine refers to restricting the movement of people who have been exposed to a virus.
- Nasopharyngeal smear: A long, flexible rod with a soft swab that is inserted deep into the nose to collect samples from the space where the nasal cavity meets the throat. Samples for coronavirus tests can also be taken with swabs that don't go as deep into the nose – sometimes called nasal swabs – or with swabs from the mouth or throat.
- Polymerase chain reaction (PCR): Scientists use PCR to make millions of copies of genetic material in a sample. With the help of PCR tests, researchers can detect the coronavirus even when it is scarce.
- Viral load: The amount of virus in a person's body. In people infected with the coronavirus, viral loads can peak before symptoms, if any.
How to Think About Risks
Even so, it is often unrealistic to avoid other people for months. People have to work and attend to their basic needs, and they also crave connections with family and friends. Risk is a spectrum, not binary, and there are ways to reduce it, experts said.
"Don't let the perfect become the enemy of the good," said Dr. Anthony S. Fauci, the nation's leading expert on infectious diseases, in a New York Times interview with Elisabeth Rosenthal. “The risk of having everyone tested before you sit down for dinner is dramatically reduced. It may never be zero, but we don't live in a completely risk-free society. "
Dr. However, Fauci will not see his three grown daughters on this Thanksgiving Day.
Dr. Michael Mina, an epidemiologist and immunologist at Harvard, said that at this point in time, the pandemic could not be expected to completely eradicate the risk of coronavirus. He compared it to the risk of a car accident. To avoid any risk, people wouldn't get into a car at all. Seat belts, airbags, and traffic law compliance reduce the risk, but they don't mean someone is completely safe – and people don't stop using a seat belt just because the car has airbags. Coronavirus precautions like testing, distancing and masking work the same way, he said.
How to reduce the risk and still collect
Before meeting others, Dr. Mina, people could combine a negative test with a two-week quarantine if they are able and have an open conversation with older family members about the risk and willingness to participate. At a gathering, he said, risk reduction strategies could include keeping dinner short, hosting the event outdoors, wearing a mask when not eating, and giving air hugs instead of touching it.
Jeffrey Townsend, a professor of biostatistics at the Yale School of Public Health, said it was an effective tool to stay out of contact with other people for a week or more before taking a test. Not only does it reduce exposure, but it also gives the virus more opportunities to get detectable levels in infected people, his research found.
"You can do more quarantine and it's very helpful," he said. "But the test on leaving really helps and really drops your chance."
Professor Townsend will be celebrating this Thanksgiving Day at home with his wife and children. Although he studies test protocols, he never did a coronavirus test himself as he stayed at home except for urgent needs throughout the pandemic.