New tests for respiratory illnesses can look for more than 20 pathogens at a time.

This so-called quad test, now available at thousands of hospitals and clinics around the country, could detect not only the coronavirus, but two types of influenza and the respiratory syncytial virus, or R.S.V.

The Sanford Health system, which includes 46 hospitals and 1,400 physicians in South Dakota, carries out 600 to 800 tests for the coronavirus a day in its clinics using antigen tests, which detect proteins made by the virus.

But according to Rochelle Odenbrett, the senior executive director of laboratories, the organization is now in the process of replacing all of those tests with the quad tests used in its emergency settings.

Unlike the antigen tests, the quad test looks for a virus’s genetic material using a polymerase chain reaction, or P.C.R.

The quad test used by the Sanford system is made by the California-based company Cepheid, which received emergency authorization from the Food and Drug Administration in late September.

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.

test that looks for the coronavirus as well as 21 other viruses and bacteria simultaneously.

Doctors and test developers are still grappling with how many pathogens to test patients for in different settings.

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.