Let’s face it, if you’ve been staying home a lot, you’re probably pretty tired of looking at the same faces. Love them as we do, it feels like well past time to start seeing other people, to visit or host relatives and dear friends. So how can you do this without unknowingly spreading the virus or getting exposed?
Recently my husband and I debated this when our son, who lives in another state, said he’d like to come home for a visit. He lives with roommates in a city with a high rate of infection, and he works in a restaurant. We thought of having him get a diagnostic test to find out if he is infected. That way, if he got back a negative test, our problems would be solved, right?
Well, when I called up a few infectious disease specialists to ask if this all made sense, I discovered that using a diagnostic test for the coronavirus this way can be problematic. Here’s what I learned.
First, which test are we talking about?
Currently, the most commonly available test that can detect an active infection is the molecular or PCR test, typically collected via a swab in the nose or the back of the throat. These tests look for the virus’s genetic material — and are highly sensitive. Another kind of diagnostic test is an antigen test that can detect the coronavirus’s proteins — these are less sensitive, says Daniel Green, a pathologist at Columbia University Irving Medical Center, and can be less accurate. And finally, there are tests that show if your body has developed antibodies because it fought an infection from the coronavirus. Those tell you about an infection you had in the past, not what you have right now.
If I get a negative result on a PCR diagnostic test, can I be certain I won’t infect someone I want to spend time with?
Like everything with this pandemic, the answer is complicated. The infectious disease experts I spoke to told me there are two reasons why testing might not be very helpful. The first has to do with the length of time it takes to get your test results back these days — up to a week or more in some places for PCR tests. By the time you get your results back, you could have unknowingly been exposed to the virus, making the original test irrelevant.
The next big reason has to do with accuracy. While the PCR test is highly accurate in a laboratory setting, out in the real world it can produce some false positives and a lot of false negatives. In fact, studies show a negative diagnostic test result can be wrong between 5% and 40% of the time, depending on the circumstances.
Some of this variation has to do with how well the sample was collected — whether an adequate amount of mucous made it onto the swab, for example. But it also has to do with timing. You see, the diagnostic test tells you whether or not you have the virus on the day you took it. It reflects a single “pinpoint in time,” says Dr. Henry Anyimadu, an infectious disease specialist with Hartford HealthCare Medical Group at the Hospital of Central Connecticut.
“Suppose that I was exposed on the 1st of August and I didn’t know it,” says infectious disease specialist Dr. Aileen Marty of Florida International University. “And I took the test on the 2nd of August. My test result will probably be negative.” That’s because the virus typically has at least a four- to the five-day incubation period, so in the first few days after exposure, there may not yet be “enough virus in the upper respiratory system to be detectable,” Marty says.
Wait, up to 40% false-negative sounds like a lot — is there anything I can do to ensure my results are more reliable?
Yes, there are some things you can do. But first remember this, for many of us that false-negative rate could be much lower than 40%, says Green, who was a co-author on one of the studies about test reliability. He points out that many of the people in his study were sampled too early before the diagnostic test could detect the presence of the virus. So if you want to make sure your test is as reliable as possible, wait several days from the last point you think you could have been exposed before getting the test — and while you wait, self-quarantine to avoid further exposures.
Marty agrees, saying, before you take the test, “be in a bubble for at least four or five days.” Don’t go to bars and restaurants and scale back grocery store visits or have food delivered. The bottom line, limit your exposure as much as possible leading up to test day. And then, Marty adds, “Stay in the bubble until you get your results back.” That’s because if you aren’t careful, you could be exposed to the virus while waiting for results, and if you do have the virus — even if you don’t have symptoms — you could spread it to others.
So if negative results are iffy, is it ever worth getting a diagnostic test?
Yes. There are definitely times when one should get a test, Anyimadu says. “If you’re worried you have COVID-19 based on symptoms, you should get a test.” Or, if you think you might have been exposed — for instance, if your roommate, housemate, or someone close to you is infected — get a test.
And you should consider a test if you’ve traveled to an area with a high rate of coronavirus infection, Anyimadu says. To find out if your county or one you’ve spent time in recently has a high rate of infection, check this county-level map. If the county has more than 10 new daily cases per 100,000 residents, that’s considered high risk.
If I test positive, but I don’t have any symptoms, what should I do?
If you get a positive test result, our experts say, this is not the time to expand your bubble! Even If you don’t have any symptoms, you are possibly contagious, and you could still develop symptoms. Marty says you should isolate yourself for 14 days, learn the symptoms of COVID-19, and monitor yourself. If you do get sick and your symptoms are getting worse, call your health care provider. And don’t forget all those folks who live with you. They too need to be tested whether they have symptoms or not, Marty says, and should self-quarantine.
Marty also suggests people “connect with their department of health to assist with contact tracing,” and help health workers reach out to anyone else who might have been exposed to you.
If you develop any symptoms, keep track of when they kick in so that you will know when you’re no longer contagious. According to the Centers for Disease Control and Prevention, you should isolate yourself for at least 10 days after your first symptom appears. At that point, as long as you haven’t had a fever for at least 24 hours and you’re feeling better, you should be able to mix with others.
If I can’t rely on negative test results, what do I do instead to visit someone safely or merge social bubbles?
The safest and simplest thing to do if you want complete peace of mind is to quarantine yourself for 14 days before the visit — this is especially important if you’re hoping to visit someone who is older or has an underlying condition.
But short of that, experts say testing can play a role in your decision-making as long as you “don’t treat a negative test as a get-out-of-jail-free card,” Green says.
Think of it as one more piece of imperfect information that you can add together with the most important factor, your own behavior. Have you been able to isolate as much as possible before the potential visit with a friend? If you have gone out, did you carefully socially distance and wear a mask? Have you been avoiding bars and restaurants and indoor gatherings?
If the answer to these questions is yes, and if you are certain you haven’t been around someone with a possible or confirmed case of COVID-19, then a negative test could be helpful. “If you aren’t sick or don’t have any particular reason to believe you’re infectious,” says epidemiologist Justin Lessler from Johns Hopkins University, “then getting that negative test should increase your confidence.”
And remember, before you head off on your trip or join friends for an indoor gathering, ask the people you’re visiting about their own behaviors and whether or not they’ve also got a test. Remember, you can spread the virus, but you can receive it as well.
“There’s no way to bring your risk down to zero,” Anyimadu says. But the recommended measures of mask-wearing, social distancing, and thorough hand washing are still the most important defense against the virus. And that is true whether you’ve had a negative test, a positive test or not even gotten a test at all.
Rob Stein and Carmel Wroth contributed to this report.