“We in the laboratory are preparing for another big boom in testing,” said Dr. Baird, whose team has run more than two million coronavirus tests since the beginning of the pandemic. “Even if people are vaccinated, they’re going to wonder, ‘Am I the breakthrough case?’”
In addition to Cepheid, other companies have developed tests that look for influenza and the coronavirus at the same time, including Roche, which has received emergency use authorization for a test that looks for the coronavirus, influenza A and influenza B at once.
In recent years various hospitals have developed in-house versions of these combination tests as well, some of which look for more than a dozen different respiratory pathogens simultaneously using P.C.R. technology. Those “multiplex” tests are especially helpful in diagnosing illnesses in people with weak immune systems because they allow doctors to swiftly discern what pathogen is making a person sick before it is too late to start the right treatments.
A French company, bioMérieux, sells a P.C.R. test that looks for the coronavirus as well as 21 other viruses and bacteria simultaneously. And Roche recently bought a company that sells a machine that can screen for more than 20 pathogens in one go.
Testing for multiple pathogens does not always lead to a simple treatment, however. Co-infections, in which a person is infected with multiple viruses simultaneously, are more common than doctors expected, and sometimes the multiplex tests might detect a viral infection but miss a bacterial one, said Dr. Daniel Griffin, chief of infectious diseases at ProHealth New York. A patient could carry the influenza virus but also test positive for a bacterium such as pneumococcus, for example.
“We initially thought that every time we identified a virus, we would just be able stop all antibiotics and just treat the virus if effective antiviral therapy was available,” Dr. Griffin said. “We now know that we often need to continue antibiotics,” he explained, because sometimes the multiplex tests are not sensitive enough to rule out a bacterial culprit.
Doctors and test developers are still grappling with how many pathogens to test patients for in different settings. “A burning question at every company is what panel is best — is it one, two, four, 20?” said Dr. Mark Miller, chief medical officer at bioMérieux. Relatively young and healthy adults might just need a quad test to know if they should start on Tamiflu for influenza, for example, but patients with underlying chronic diseases who are very sick might benefit from receiving the test for 22 different pathogens so that doctors can decide whether they need to be admitted to a hospital.