Is Sharing a COVID Test a Bad Idea, or Just a Gross One?
“It started as a joke, actually,” Elena Korngold told me. But late last month, the 40-something radiologist from Portland, Oregon, and her family decided that their unsanctioned scheme couldn’t hurt. Elena began the proceedings by unwrapping the sterile swab from a BinaxNOW rapid test for SARS-CoV-2, part of the family’s dwindling supply. She swirled the swab around the insides of each of her nostrils. Then she passed it to her husband, a cardiologist named Ethan, who swirled it around the insides of each of his nostrils. Then their two children did the same. It was “like some sort of religious ritual,” Elena said.
The snot-saturated swab went into the test card. The test card showed a negative result. The Korngolds, now bonded by something even thicker than blood, went to their dinner party. Nobody got COVID.
Ethan came up with this system on his own, but other people have had similar ideas. Since the Omicron variant began its high-speed march across the United States, at-home tests have become nearly impossible to find in many towns and cities. So some Americans—half-proud, half-embarrassed, and fully desperate to find out whether they’re infected—have tossed the rapid-test instruction manual. To stretch their resources, they’ve started combining samples in their home. When a group test is negative, they conclude that everyone is in the clear, and several testing kits can be saved for future use; if that test is positive, further diagnostics will ensue. But experts say that using rapid tests like this, off-label, won’t produce reliable results. Also, sticking the same swab up multiple noses is, to put it scientifically, gross.
The family rapid testers draw their inspiration from pooled testing, a well-established and efficient method used by schools, sports leagues, and hospitals to screen for the virus. In standard pooled testing, people without symptoms might be divided into, say, groups of 10. Mucus from each person is collected (using a fresh swab; I guess I have to specify that now). A lab mixes together a bit of each sample from the group of 10, and then tests the witches’ brew using the PCR method. If a pool is positive, each individual specimen can be retested to figure out who’s carrying the virus.
Pooled PCR testing works because the process was designed with that in mind, Jennifer Nuzzo, a senior scholar at the Johns Hopkins Center for Health Security, told me. The samples are each mixed with just the right amount of chemicals to combine into one working test. Squeezing swabs from multiple people into a kit designed to test just one “isn’t really pooled testing,” she said. The rapid tests currently available to Americans don’t come with all the swabs, chemicals, and test tubes that would be necessary to accommodate multiple samples, and jerry-rigging that equipment could lead to contamination or unwanted chemical reactions. Susan Butler-Wu, a clinical microbiologist at the University of Southern California’s Keck School of Medicine, told me that the inclusion of too many human cells from the insides of too many human noses could also produce false negatives on antigen tests by diluting the virus sample. The latter problem doesn’t apply to PCR tests, for which samples are washed of irrelevant genetic material.
Then there’s the ick factor. “From a public-health perspective, the idea of sticking swabs up each other’s noses doesn’t sound like a great thing to do,” Nuzzo said. If one person in a household gets COVID, the others aren’t doomed to infection just from living in the same space. In fact, the “secondary attack rate” within a home—which describes the chance of transmitting a virus from one household member to another—appears to be just 15 to 35 percent for SARS-CoV-2. But intranasal promiscuity is a surefire way to increase those numbers, Nuzzo warns, and spread untold other germs besides.
Imagine that no one in a family of five has any COVID symptoms, and they have only one test. Imagine also that the family is on their way to visit Grandma. Would a pooled test make a little bit of sense in that scenario? Just a teeny, tiny little bit? Nuzzo doesn’t think so, because scientists have no way of guaranteeing that the test would pick up on a positive case within that family. All five people might conclude that they won’t give Grandma COVID, but that’s not actually what the test was designed to show them. Instead, Nuzzo said, the one test should be used by the person in the house who’s most likely to have been exposed, such as a child attending school or a parent who works in health care or the service industry.
The problem isn’t that pooled rapid tests definitely don’t work; it’s that they don’t definitely work. The tests available to Americans are in “a total data-free zone” in this regard, Nuzzo said. Some studies of pooled rapid testing have been carried out on kits that aren’t yet FDA-authorized, though—and their results are promising. A group from E25Bio published a study this summer showing that its rapid test can pick up on one positive, symptomatic sample among a group of 19 negatives. Another group, in Germany, used materials from two existing rapid tests to build a prototype of a pooled rapid test that could detect positive samples among as many as six swabs. Both studies did suggest that pooling rapid tests made them somewhat less sensitive, however.
Bobby Brooke Herrera, the chief science officer at E25Bio, who led the company’s study, told me that his team’s results are not an invitation for consumers to “go rogue,” because the current FDA-authorized kits simply aren’t set up for pooled testing. The Korngolds had to share a single swab for their BinaxNOW pooled test and then insert it into the testing card. If they’d had a tube-based test instead—like the QuickVue test from Quidel—they could have stuck four separate swabs into a single vial of buffer solution. But even then, each swab would have absorbed some liquid when it was swished around, Herrera said. “By the time you put the fourth swab in the buffer, you’re probably going to have no buffer left.”
Still, with the right tweaks, some of these tests might become poolable. “I’ve been really frustrated that none of the test makers have given instructions for, or provided extra swabs for, or given any indication that it would be okay to pool,” Michal Tal, an immunologist at Stanford, told me. Because of its lower sensitivity, a pooled test might not catch an infection as early as an individual test would, she said, but if pooling allows a family to test more often, they could still come out on top.
Tal has made use of pooled rapid testing herself. Unlike the Korngolds, she and her co-testers applied their own swabs, which Tal bought online after making sure they matched the ones included with the test. She was just as horrified at the prospect of sharing mucus as all the other experts I spoke with, calling it both “unsafe” and “gross.”
The Korngolds considered—and then put aside—the possibility that their testing experiment could speed infection from one person to another. “It seemed like it would be a reasonable thing to try,” Ethan told me. After all, each of them was up to date on their vaccines, and if the pooled test did come back positive, they had enough tests in the house to identify the culprit. They didn’t even have any trouble working out their order of snot transmission. (Ethan: “We’re close enough as a family that there really couldn’t be any other way.” Elena: “Every family probably has an order in their own mind.”)
In the grand scheme of pandemic-induced norm-breaking, the Korngolds said, the shared nose swabbing hardly registered against changes like remote schooling and reusing masks in the hospital. And in the grand scheme of being a family, well, they’ve seen worse. “I would say it is not one of the grossest parts of parenting by a long stretch,” Elena said.
The Korngolds insisted that they know perfectly well that their DIY pool setup might not be as accurate as testing one person with one kit, but they don’t regret giving it a go. “I think we’re just like other families that are trying to figure out a way through this,” Ethan told me. And if they get desperate, he and Elena said, they’d happily share snot again.