Fighting COVID with a swab: testing remains a vital weapon in saving lives - Salish Current
October 16, 2020
Fighting COVID with a swab: testing remains a vital weapon in saving lives
Alex Meacham

The cotton swab is a primary tool in a widely used test for COVID-19, and a vital part of the strategy being deployed to help keep the virus from spreading. Above, a detail from instructions for a kit for taking test samples illustrates one of many resources available from the Centers for Disease Control.

photo: Centers for Disease Control © 2020
October 16, 2020
Fighting COVID with a swab: testing remains a vital weapon in saving lives
Alex Meacham


What does it mean to get a negative COVID-19 test result? It means an unmasked sigh of relief, that once again, in a year fraught with worry, there’s one less thing to be actively worried about.

The negative result, however, does not always mean that the virus isn’t present. Nonetheless, testing is an important part of the strategy to help stanch the spread of COVID-19.

Frank Ameduri, public information officer for the Washington State Department of Health said “in general we don’t really track false negatives or false positives either,” meaning that nobody at the state level is really quite sure how many people are going about their lives thinking that they aren’t carrying the virus, when they are. 

At this point, we don’t have a good way to track statewide … a negative test [followed by] a positive test.

Erika Lautenbach

Locally, Erika Lautenbach, director of the Whatcom County Health Department, said the state has been working in partnership with local governments to try to find these false negatives. She concludes that the data analysis problem exists because the group of people that could be identified as false negatives includes people who are testing many times. If everyone were tested only once, the percentage would make sense.

According to Lautenbach, Washington state calculations are based on individuals testing positive or negative, rather on than the number of negative and positive tests. The latter method would allow for calculating false negative tests. 

“At this point, we don’t have a good way to track statewide … a negative test [followed by] a positive test” in the same individual, Lautenbach said.

How positive or negative?

Health officials are more concerned with the accuracy of test types. The type of test that is most routinely performed is the polymerase chain reaction, or PCR, test. The PCR test is very specific, but sometimes has problems with sensitivity. High sensitivity means that a test that shows a positive result is very likely to be correct, but that a negative result may be wrong. It also takes more time to run PCR tests, which can be a disadvantage. 

Some localities are using less specific tests (in which a positive result may be wrong more often) to inform if someone should be tested using the slower PCR method. The less specific testing methods are much faster, in the realm of minutes rather than days. 

According to research published in June, the PCR test can vary in accuracy from 11% to 40% false negative results, depending on where the sample is taken (typically, nose, mouth or throat); with a false-negative rate of 27% from nasal swabs. That means that if a person is infected and receives a negative result, there’s still a 27% chance that the result from a nasal-swab PCR test was wrong.

The same paper suggested that in general, most PCR test could be assumed to be about 70% sensitivity — that is, the test result will be positive in someone who is infected.

Under certain criteria, 10% of COVID-19
samples can be expected to yield
negative results regardless of whether
the virus is present.
(Alex Meacham graphic © 2020)

Ryan Fortna, the Molecular Laboratory director at Northwest Laboratories in Bellingham, said that in a sample of 100 infected people, tested in three different viral sites, at least 10% will come back negative, no matter what.

As for the rate of false negatives, Fortna said that the data might exist, but the calculation would mean a lot of database analysis. It would take up the time that he and his colleagues could spend finding positive tests and helping to slow the pandemic. He also said that there’s really no way to know if it was a false negative or an infection after the initial test. 

Relief? Or anxiety?

For an individual, testing can be a relieving yet stressful experience, bringing ambivalence about whether to feel anxiety or happiness.  

Take for example, Marybeth Manning, a Bellingham resident preparing for a visit from family from California. Her daughter was tested before leaving, and, to be extra careful and protect each other, Manning wanted to get tested as well. So she and her husband signed up through the online portal to be tested at the Skagit drive-through testing location.  

The system automatically assigned a physician, who, based on Manning’s lack of presumed exposure, called for a nasal swab. If there was some reason to assume that Manning had been exposed, the physician likely would have called for a nasal pharyngeal swab —  the longer, more intrusive kind; the kind that feels like the testing staff are swabbing brains. 

At the testing site, the couple gave their information to the staff and were handed swabs to sample themselves. Like most tests being run in the area recently, it was a simple nasal swab: ten seconds in each nostril, on the same stick, handed back to the staff; and then they drove off. Manning said it took about 20 minutes in all. 

To be extra cautious, they had planned on quarantining for the next two days. Due to processing errors, for which they never received any explanation, they didn’t get results for four days. Their family arrived after three days, so they did their best to quarantine in their own house and wore masks when they couldn’t. 

Two days after following up with the health department about the wait, Manning got a text: negative. 

Paying attention, saving lives

This is where the story would change for someone who was a false-negative tester, which, to be clear, Manning was not. 

Imagine another person — call him Jim — in the same situation as Manning.

Jim has had a test and received a negative result. But subsequently he has had a headache for a few days. He’s taken some ibuprofen when it was bad, but for the most part, has lived with it. Jim wants to be extra safe and had seen a post on social media saying that a headache can be an early symptom. He schedules another test. Two more days pass, and Jim still has a headache. His results come back: positive. 

Jim now must quarantine for 10 days past the onset of symptoms, and then for another 24 hours after he has no symptoms.

Neither story is unusual. In a common scenario, the amount of virus in Jim’s system, or perhaps just at the site that was first swabbed, was not high enough to be detected by the test at that time. 

If Jim hadn’t had — and paid attention to — that headache, because he was otherwise asymptomatic, he could have infected countless others as he went about his routine life, including his family. Imagine if Jim worked in a grocery store, restaurant or school. That is the danger of a false negative. By listening to his symptoms, Jim would have saved lives.

— By Alex Meacham


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