So-called quad tests, now available at thousands of hospitals and clinics, can detect not only the coronavirus but also two types of influenza and the respiratory syncytial virus, or R.S.V.
That might not seem essential given that the United States, like many other countries, witnessed a shocking absence of a flu season this past winter. But as the country begins to reopen, doctors say that flu and other pathogens could make a comeback this fall.
What’s more, even as a growing number of people get vaccinated against Covid, there are still some 40,000 new infections every day in the United States, so testing will still be in demand.
Unlike the antigen tests, the quad test looks for a virus’s genetic material using a polymerase chain reaction, or P.C.R. The P.C.R.-based method is far more accurate than the antigen approach, though P.C.R. sequencing of patient samples used to be more cumbersome and relied on multistep procedures.
Several factors might precipitate the flu’s return in the fall: children returning to school, declining use of masks, and perhaps a lack of recent immune system exposure to the flu. If more people get sick in the fall, they will want to know if it is flu or coronavirus.