The U.S. has conducted some 52 million COVID-19 tests, but it’s still not enough. Many epidemiologists believe that broadly testing people with or without symptoms is the way to root out cases of COVID-19 and develop better strategies for curbing the spread of the disease. To do that, public health experts are now discussing a technique called pooled testing—testing a batch of human samples together for COVID-19.
The Food and Drug Administration recently awarded Quest Diagnostics with emergency use authorization (EUA) for its pooled testing method. It essentially allows the company to take four individual samples and run them together on its machine. Lab Corp, which recently had the EUA for its test expanded to include pooled testing, is able to run up to five samples at a time. There is potential to scale that up more; one investigation into pooled testing suggested that as many as 64 samples could be run together with 96% sensitivity, so long as the test is calibrated accordingly. Once the samples are run, the machine identifies if there is viral RNA in the group. If there is, doctors can run additional tests to determine who is infected. If not, doctors can quickly know the group is COVID-19 free. The hope is this will increase the number of people who get tested. Quest is now rolling out its pooled test in Chantilly, Virginia, and Marlborough, Massachusetts.
This way of pooling testing aims to increase testing capacity, so that labs can handle more tests at once. But there are other ways to run a pooled test.
“This is not how it would work but imagine 50 people spit in a bucket. It all gets stirred up, no samples are specific to the person, then you test the bucket,” says CEO and cofounder of Gingko Bioworks, Jason Kelly. He says that Quest’s test is a way of speeding up diagnostic testing. By running samples in batches, the company is more quickly able to determine that several people are negative (ideally). What Gingko Bioworks is aiming to do is develop surveillance testing for schools and workplaces.
Surveillance testing is a way of understanding whether a disease is present in a community by regularly testing a pool of samples. One way of doing this is through sewage testing. If a community tests its waste water for COVID-19 every week, let’s say, public health officials can spot the virus in a community and strategize how to get ahead of an outbreak. Another method of surveillance testing is through a pooled test like the one Kelly describes, where a large group submits a collective sample at a decided-upon cadence. Through regular group testing, doctors and public health departments can see where clusters of cases might emerge. Pooled testing and sewage testing also allow doctors and public health officials to better account for asymptomatic cases, which are unlikely to have shown up at the doctor’s office.
Kelly and his team have been building a facility that he expects will be able to process 250,000 pooled samples a day with a 24-hour turnaround time. Once the facility and its test have emergency use authorization from the FDA, Gingko Bioworks will start testing in Massachusetts, where the company is based, and expand within the Northeast. Kelly says that if the U.S. wants to reopen the economy and bring kids back into schools, it will be necessary to have some kind of surveillance testing to understand where the disease is about to break out in order to take steps to mitigate the number of cases.
We need to build surveillance or else we’re going to go through this up and down up and down [of cases].”
“We need to build surveillance or else we’re going to go through this up and down up and down [of cases] and open, close, open, close [of the economy] until we have a vaccine,” he says. Kelly’s hope is that Gingko Bioworks’s effort will strategically increase testing capacity in the U.S. by bringing his company’s pooled testing method to schools and workplaces.
The focus on pooled tests comes as the U.S. struggles to identify new cases of COVID-19 and contain its spread as cases and deaths continue to rise in the South and West. But even though the coronavirus continues to spread, there is no federal strategy around testing for COVID-19. Nowhere in this country is it required for anyone to get a COVID-19 test.
Even though increased testing of all kinds could help with the country’s coronavirus response, more traditional testing remains rife with issues. In the early days of the virus, testing was famously restricted to those with symptoms. While that is no longer the case—lots of doctors’ offices are offering tests to whoever wants one—various locales are also experiencing a backlog in testing, meaning patients aren’t getting their results for days and sometimes weeks. Such delays render those tests almost useless. Tests that indicate the presence of a virus in your system are merely a snapshot in time. When the disease is as rampant as it is in the U.S., a person can get sick at any moment, making a negative result hardly an assurance. Who cares what your diagnosis was on Monday if by Friday you’ve had a whole new set of interactions during which you could have been exposed to COVID-19? In addition, the COVID-19 molecular tests also have a fairly high false-negative rate, making repeated testing important.
For all these reasons, a number of doctors are advocating for surveillance testing.
“My own feeling is that the frequency of testing—especially with all of the asymptomatic carriers that are likely out there—is that really we should work from the point of view of how can the greatest number of people get the greatest number of tests,” says Dr. Stephen Wilson, executive vice president and COO of La Jolla Institute for Immunology in San Diego California. “The logistics should be designed around that.”
We should work from the point of view of how can the greatest number of people get the greatest number of tests.”
Wilson says that if pooled testing is how America will be able to achieve broader testing, then he thinks it could be a worthwhile endeavor. Of course, as with all testing methods, there are drawbacks. With pooled testing there is a concern that samples may become so diluted that the test won’t be able to pick up on a small amount of virus. Wilson says that test makers can build around that problem by finding the vanishing point in their test, essentially determining how many samples dilute the pooled sample so much that the test isn’t able to accurately detect the virus.
There also should be some consideration for how pooled testing is used. Ideally, it would be used on groups of people who are in close physical contact rather than a bunch of samples randomly pooled together at the doctor’s office, Wilson says. This would also help with contact tracing efforts.
Another point he raises is that pooled testing only cuts costs if a significant number of pooled tests come back negative. “If there’s a positive in a pool, you need to test all the samples anyway, so does it speed things up?” he asks. If a community is suffering through an outbreak, it may be more important to ramp up individual testing than to conduct group testing. However, doing surveillance testing, such as a sewage or otherwise pooled test, in conjunction with individual testing would be able to tell public health officials when the virus has been sufficiently beaten back.
Ultimately, Wilson thinks that surveillance testing could not only help inform public health decisions, but also how individuals navigate the pandemic themselves. “I try to think back to the days before we could really do this kind of thing—in the days of polio,” he says. He says if pooled testing had been available then, parents would have been able to know whether there was polio circulating in their schools or in their communities. If they had had that information, maybe they would have made different decisions about sending their kids to school. “Maybe they would have held off one more year knowing the polio vaccine was going to be out,” he says. “I think they would have liked to have maybe held their kids off.”