Will those who recover from covid-19 be able to vote?
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(CNN) -
If you think a negative COVID-19 test result means you don't have coronavirus, you could be wrong.
It can take days before a new infection appears in a coronavirus test.
“We know that the incubation period for covid-19 is up to 14 days.
And before that, the test can be negative and you can have no symptoms, "emergency medicine doctor Leana Wen told CNN.
"But you could actually be harboring the virus and be able to pass it on to others."
So if you want to get tested as a precaution before seeing friends or family, here's what you need to know.
Questions from the audience about coronavirus: the tests that people who overcome the covid-19 should take
Deadly mass events are spreading covid-19 3:26
If I was infected yesterday, would a test today detect the virus?
Probably not.
A study in the Annals of Internal Medicine medical journal examined false negatives from tests of people who actually had COVID-19.
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The study estimated that during the four days of infection before symptoms appeared, the probability of getting an incorrect / negative test result on day 1 was 100%.
The day people started showing symptoms, the average false negative rate dropped to 38%, according to the study.
Three days after symptoms began, the false negative rate dropped to 20%.
"The virus just takes time to replicate in the body to detectable levels," said Justin Lessler, lead author of the study and associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.
"You can become infected with a few virus particles, but these will not be detectable until they have time to replicate at levels adequate to be detected," he told CNN by email.
So how many days should a person wait after a possible exposure to get tested?
"There is no hard and fast rule of thumb, but the evidence suggests that getting tested before the third day after exposure is not very helpful," Lessler said.
Could it be contagious if the test is negative?
Absolutely.
“People feel that if the test is negative they are out of danger.
And the truth is, no, "said Dr. Rochelle Walensky, chief of the division of infectious diseases at Massachusetts General Hospital.
For people who get sick with COVID-19, symptoms can take up to two weeks to appear, but the average time is about five days, Walensky said.
"In general, the two days before that day and the two days after that are thought to be most contagious," he said.
One of the reasons this virus spreads so easily is because people can spread it without having symptoms.
The US Centers for Disease Control and Prevention (CDC) estimate that 40% of infections are asymptomatic and 50% of transmissions occur before symptoms begin.
“It has been one of the biggest Achilles heels of this.
And it has been among the biggest challenges and the unexpected because with other similar viruses, this is not true, "said Walensky.
"The reason we were able to control the SARS outbreak so quickly, even though there were obviously a lot of deaths there, but it didn't turn into a pandemic, is because people didn't spread the virus until they had symptoms."
Do the different types of covid-19 tests matter?
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This you should know 1:19
When it comes to diagnostic tests - those that detect if you have an active coronavirus infection - there are two main types:
Molecular tests,
like PCR tests, look for the genetic material of the virus.
Most of these tests are done with nasal or throat swabs, although some can be done with saliva,
says FDA
.
"This test is usually very accurate and usually does not need to be repeated," says the FDA.
But the downside to molecular testing is that results can take a while, from the same day to a week after the test.
"For people showing symptoms, studies so far show that the precision of molecular testing in finding a positive case increases every day after exposure," said Pia MacDonald, infectious disease epidemiologist at the nonprofit research institute. RTI International.
But for infected people with no symptoms, the accuracy rates are less clear, he said.
"Performance studies of molecular tests in asymptomatic people are very limited."
Antigen tests
are often referred to as rapid tests (although some molecular tests are also rapid).
Antigen tests are not antibody tests, which indicate whether you have had the virus before and have already developed antibodies against the infection.
Antigen tests do not look for the genetic material of the virus, as molecular tests do.
Instead, they look for specific proteins on the surface of the virus.
The good news is that antigen test results can be obtained in less than an hour.
The bad news is that you are more likely to get a false negative with a rapid antigen test.
"Positive results are usually very accurate, but negative results may need to be confirmed with a molecular test," says the FDA.
"Antigen testing is more likely to miss an active coronavirus infection compared to molecular testing."
This could help explain some of the recent Covid-19 spread linked to the White House.
While staff members close to President Donald Trump and Vice President Mike Pence are tested frequently, White House staff often use rapid antigen tests, which generally have a higher false-negative rate than the tests. molecular.
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Regardless of the type of diagnostic test you use, you are generally more likely to get a false negative than a false positive.
"If a molecular test is positive, it is an accurate reflection of a person's infection," MacDonald said.
«If it is negative, it is less trustworthy that the person is really negative.
The same goes for antigen tests. '
Can I take a test at home?
Yes. There are some home test kits available, such as the Everlywell covid-19 molecular test.
Users take their own nasal swab samples and mail them to a laboratory, which will send the results digitally within 24 to 48 hours of receiving the samples.
But running any kind of COVID-19 test too early could miss an infection, said Dr. Frank Ong, Everlywell's chief medical and scientific officer.
"As testing capacity has continued to increase, more and more asymptomatic or mildly symptomatic people have been tested, most of them probably with lower viral loads in their clinical samples," he said.
“My best advice is to treat yourself as if you are probably infected after a suspected exposure.
Self-quarantine yourself, wear a mask to cover 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-cleared test for covid-19.
So what should I do if I want to see friends or family?
If you insist on seeing your loved ones by Thanksgiving, self-quarantining for 14 days in advance is probably your safest bet, Walensky said.
"After a real 14-day quarantine, if done correctly, you don't need a test," he said.
That's probably the cleanest way to do it.
To be clear: self-quarantining means staying home.
It doesn't mean you can run errands.
"'Grocery store' and 'quarantine' cannot be combined," Walensky said.
Adding tests to your list of precautions "is helpful, but only if done correctly," he said.
"And if you don't know exactly when or how to use it, you may well be setting yourself up for a false sense of security."
Lessler agreed that quarantine is for the best and testing should be done wisely.
"If you are visiting an elderly relative and you have a reasonable risk of being exposed, there is no option for the 14-day quarantine," Lessler said.
“At least I would wait 10 days and get a negative test.
If you are visiting a younger, healthier relative and have little chance of being exposed before or during the trip, then 5 or 7 days (quarantine) plus a test is probably a large risk reduction, although it does not guarantee safety.
Either way, you definitely need to stay in quarantine while you wait for the test results and make sure that everyone you meet is on the same page about the plan to control the risk of infection.
There have already been cases of the coronavirus spreading within families within days after a person tested negative, said Dr. Michael St. Louis, a member of the CDC's Community Counseling Team.
He said everyone should remember to treat family the same way they would treat their friends or unrelated coworkers during this pandemic.
Of course, the best way to help ensure the safety of all your loved ones is to celebrate the holidays remotely.
"I have three children… And my parents will not be joining us this year," Walensky said.
It's just horrible.
But I put up with it because my parents are pretty healthy, and I would never forgive myself if I put them in danger.
And I'm looking forward to 2021 in which we can be together.
The CDC suggests celebrating with your loved ones virtually online.
You can also prepare traditional Thanksgiving dishes and deliver them "in a non-contact way" with family, neighbors, or those who may feel alone.
Walensky said the little sacrifices made this Thanksgiving will help ensure everyone is healthy enough to sit at the table next year.
"At least they will be there next year, whereas irresponsible behavior now could mean they weren't there later," he said.
"Let's do this so we can have a better chance of being around the table together, healthy, in 2021."
- CNN's Lauren Mascarenhas contributed to this report.
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