“We’re preparing for another big test boom in the lab,” said Dr. Baird, whose team has carried out more than two million coronavirus tests since the pandemic began. “Even when people get vaccinated, they’ll be asking, ‘Am I the breakthrough?'”
In addition to Cepheid, other companies have developed tests that check for influenza and coronavirus at the same time, including Roche, which has received emergency use approval for a test that checks for coronavirus, influenza A, and influenza B at the same time.
In recent years, various hospitals have also developed in-house versions of these combination tests, some of which use PCR technology to simultaneously scan for more than a dozen different respiratory pathogens. These “multiplex” tests are particularly useful in diagnosing disease in people with weak immune systems, as doctors can quickly identify which pathogen is making a person sick before it is too late to start the right treatments.
A French company, bioMérieux, sells a PCR test that looks for the coronavirus and 21 other viruses and bacteria at the same time. And Roche recently bought a company that sells a machine that can examine more than 20 pathogens at once.
However, testing for multiple pathogens doesn’t always result in an easy treatment. Co-infections, where a person is infected with multiple viruses at the same time, are more common than doctors expect, and sometimes the multiplex tests detect a viral infection but miss a bacterial one, said Dr. Daniel Griffin, Head of Infectious Diseases at ProHealth New York. A patient could carry the influenza virus, but could also test positive for a bacterium such as pneumococci.
“We initially thought that every time we identified a virus we could stop all antibiotics and treat the virus if effective antiviral therapy was available,” said Dr. Griffin. “We now know that we often have to keep taking antibiotics,” he said, as the multiplex tests are sometimes not sensitive enough to rule out a bacterial culprit.
Doctors and test developers are still grappling with the number of pathogens that patients should be tested for in different settings. “A burning question in any company is which panel is best – is it one, two, four, 20?” said Dr. Mark Miller, Chief Medical Officer at bioMérieux. Relatively young and healthy adults may only need a quad test to know whether to start using Tamiflu for influenza, for example. However, patients with underlying chronic diseases who are very ill can benefit from testing for 22 different pathogens so doctors can decide whether they need to be hospitalized.