Pressure to perform widespread Covid-19 testing is growing as public health experts and ordinary citizens question the safety of reopening schools and businesses across the U.S. without better information about who is infected and at risk of spreading the virus. That is only adding to the strain on the nation’s testing capacity, and raising questions about who should get priority.
The Infectious Diseases Society of America, which represents the nation’s infectious disease experts, issued guidelines Wednesday about who should be tested, how they should be tested, when they should be tested, and then what to make of the results.
Some answers aren’t known with any certainty yet, leading to knowledge gaps future research might fill, but not before many states begin to relax social distancing, two co-authors of the guidelines said in a call with reporters Friday. Meanwhile, tests and chemicals needed by labs to interpret them are still in short supply.
“Something that we’re all concerned about right now is in some locations in this country, they don’t have adequate [supplies] to test symptomatic patients,” said Angela Caliendo, an infectious disease specialist and professor of medicine at Brown University. “It remains a substantial challenge for all of us to be able to get enough people tested and having enough reagents to do that.”
Shortages go beyond tests and reagents when community surveillance is proposed as a way to judge how the coronavirus is spreading, said Kimberly Hanson, an associate professor of medicine at the University of Utah School of Medicine.
“It’s all sorts of resources around the testing,” she said. “We need more support for public health in our area to really deploy testing and contact tracing in the community. We need to train and get more epidemiologists and contact tracers to do that.”
Here’s what else Caliendo and Hanson had to say about testing:
Who should get tested?
Policies about testing all people with possible coronavirus infections have varied from state to state. But the IDSA guidelines state that all patients who have clinical signs or symptoms that could be consistent with Covid-19, as defined by the CDC, should be tested. Knowing if a patient is infected with the virus starts a cascade of decision-making for clinicians: Do they need to be hospitalized and separated from other patients? If they can go home, how should they isolate themselves?
Another reason to test patients is to see if they would consider being enrolled in a clinical trial of a Covid-19 treatment, Hanson said.
What about people who don’t have symptoms?
If there aren’t enough tests, symptomatic patients should get them, but there are three situations that argue for a test in asymptomatic patients. If a patient is already in the hospital and Covid-19 is widespread in the area, do the test. If a patient has a compromised immune system owing to a disease or a transplant, that patient should be tested because Covid-19 leads to poor outcomes in these people. And if a patient is going to have surgery, do a test for the patient’s sake and for the protection of health care workers.
What kind of test is best?
A nasal swab or a nasopharyngeal swab got the group’s recommendation, based on a review of the medical literature. Throat swabs and saliva specimens did not, but that could change as more studies are published, particularly about saliva.
The group did not find enough research to differentiate the effectiveness of rapid testing — results within an hour — from standard testing that takes up to five hours.
Most of the information about various tests is based on limited lab experiments comparing an individual test to what are called contrived samples, such as a nasal swab that doesn’t have any virus on it. The Food and Drug Administration approved tests using relaxed standards, so evaluations of tests as they’re used in the field, or comparisons among tests, have not been done.
“We don’t know yet what test is best or really how the emergency use authorization tests in the U.S. that are commercially available really compare to each other,” Caliendo said.
Should people get repeat tests?
Tests can have up to a 30% false negative rate, meaning they miss that proportion of people with actual infections. The IDSA said the need for retesting people with negative results depends on how sick the person seems to be. “If you have a low clinical suspicion and the test is negative, our recommendation was to not retest. But if you have a high clinical suspicion, you should retest people who are ill, who are in the hospital, who are in the ICU,” Caliendo said.
What about antibody testing?
Antibody tests don’t detect an active infection, but rather look for signs that a person was previously infected, as shown by antibodies their immune system produced to fight the coronavirus. With other diseases, the presence of antibodies often means you have acquired immunity against re-infection, for at least some period of time, but that is not known yet in the case of Covid-19.
“We don’t have enough information about the performance of these tests to know ideally how to use them,” Caliendo said. “We need to understand, if the test is accurate and you have antibodies, what does that mean? Does it mean you’re protected from future infection? We don’t know that. We don’t know if it means you’re no longer infectious.”
Her advice to patients who get the antibody test anyway: “If you test positive, do not assume you’re immune from the attack, do not assume that you don’t have to abide by distancing, wearing masks, washing your hands, and doing all of that.”
How much testing is enough testing? Is there a percentage of the population we should shoot for?
“I think in general more is better. But I do think resources are not limitless and there still are places in the country that really don’t have sustained access to testing,” Hanson said. But “we need to really understand at a given location how much asymptomatic infection is present.”
Crunch time for labs.
People who have been able to manage their non-Covid-19 medical problems over the past few months will eventually come back to the hospital, Caliendo predicted, for the elective surgeries they may have postponed. When they do, that will strain hospital labs.
“The clinical labs are going to get really busy again,” she said. “And they won’t have as many resources to devote to Covid-19 when surgery opens up and we get back to what we would call our previous normal.”