Why Pooled Testing for the Coronavirus Isn’t Working
Why Pooled Testing for the Coronavirus Isn’t Working
Pooling accounts for about one-third of the samples that are processed at Poplar, Mr. Sweeney said, adding “that percentage is going to get much higher.”
But in many other regions, experts are having trouble clearing the hurdles to benefit from pooling — in part because needs differ so vastly from institution to institution, and even from test to test.
“There’s been a lot of concerns about all the challenges,” said Dr. Bobbi Pritt, director of the clinical parasitology laboratory at Mayo Clinic, which processes tens of thousands of coronavirus tests each week, but has yet to roll out pooling.
Experts disagree, for instance, on the cutoff at which pooling stops being useful. The Centers for Disease Control and Prevention’s coronavirus test, which is used by most public health laboratories in the United States, stipulates that pooling shouldn’t be used when positivity rates exceed 10 percent. But at Mayo Clinic, “we’d have to start to question it once prevalence goes above 2 percent, definitely above 5 percent,” Dr. Pritt said.
And prevalence isn’t the only factor at play. The more individual samples grouped, the more efficient the process gets. But at some point, pooling’s perks hit an inflection point: A positive specimen can only get diluted so much before the coronavirus becomes undetectable. That means pooling will miss some people who harbor very low amounts of the virus.
The Coronavirus Outbreak ›
Frequently Asked Questions
Updated August 17, 2020
Why does standing six feet away from others help?
- The coronavirus spreads primarily through droplets from your mouth and nose, especially when you cough or sneeze. The C.D.C., one of the organizations using that measure, bases its recommendation of six feet on the idea that most large droplets that people expel when they cough or sneeze will fall to the ground within six feet. But six feet has never been a magic number that guarantees complete protection. Sneezes, for instance, can launch droplets a lot farther than six feet, according to a recent study. It’s a rule of thumb: You should be safest standing six feet apart outside, especially when it’s windy. But keep a mask on at all times, even when you think you’re far enough apart.
I have antibodies. Am I now immune?
- As of right now, that seems likely, for at least several months. There have been frightening accounts of people suffering what seems to be a second bout of Covid-19. But experts say these patients may have a drawn-out course of infection, with the virus taking a slow toll weeks to months after initial exposure. People infected with the coronavirus typically produce immune molecules called antibodies, which are protective proteins made in response to an infection. These antibodies may last in the body only two to three months, which may seem worrisome, but that’s perfectly normal after an acute infection subsides, said Dr. Michael Mina, an immunologist at Harvard University. It may be possible to get the coronavirus again, but it’s highly unlikely that it would be possible in a short window of time from initial infection or make people sicker the second time.
I’m a small-business owner. Can I get relief?
- The stimulus bills enacted in March offer help for the millions of American small businesses. Those eligible for aid are businesses and nonprofit organizations with fewer than 500 workers, including sole proprietorships, independent contractors and freelancers. Some larger companies in some industries are also eligible. The help being offered, which is being managed by the Small Business Administration, includes the Paycheck Protection Program and the Economic Injury Disaster Loan program. But lots of folks have not yet seen payouts. Even those who have received help are confused: The rules are draconian, and some are stuck sitting on money they don’t know how to use. Many small-business owners are getting less than they expected or not hearing anything at all.
What are my rights if I am worried about going back to work?
What is school going to look like in September?
- It is unlikely that many schools will return to a normal schedule this fall, requiring the grind of online learning, makeshift child care and stunted workdays to continue. California’s two largest public school districts — Los Angeles and San Diego — said on July 13, that instruction will be remote-only in the fall, citing concerns that surging coronavirus infections in their areas pose too dire a risk for students and teachers. Together, the two districts enroll some 825,000 students. They are the largest in the country so far to abandon plans for even a partial physical return to classrooms when they reopen in August. For other districts, the solution won’t be an all-or-nothing approach. Many systems, including the nation’s largest, New York City, are devising hybrid plans that involve spending some days in classrooms and other days online. There’s no national policy on this yet, so check with your municipal school system regularly to see what is happening in your community.
“Are we going to cause harm if we miss them? I think that’s still a difficult question to answer,” Dr. Liesman said. These people may be less likely to pass the virus to others, and may be at lower risk of getting severely ill. But that’s no guarantee. Some might simply be early on in their infection.
Pooling can also be onerous for lab technicians — many of whom have been working grueling hours for months on end. Though simple in theory, batching samples is tedious and time-consuming, as researchers carefully transfer precise amounts of liquid from one tube to another hundreds, perhaps thousands, of times over.