A health worker takes a nasal sample for the COVID-19 rapid antigen test in New Delhi, India, Friday, June 19, 2020. Antigen tests can generally detect between 80 and 90 percent of positive cases of COVID-19, the disease caused by the virus. Credit: Manish Swarup | AP

Three southern Maine nursing homes are among the nation’s first such facilities to receive free coronavirus testing machines — and some of the materials needed to use them — as part of a new push by the federal government to help them quickly detect new cases of the infection.

But some doctors who oversee the medical care in Maine nursing homes are cautioning that those testing systems aren’t the most reliable on the market and cannot fully replace a more established testing method that requires samples to be sent off to labs.

It’s also unclear how long the testing materials provided by the government will last and when facilities will be on the hook to buy more, according to the Associated Press.

The machines use technology called antigen testing, in which tissue is collected from inside someone’s nose and placed into a machine that can look for proteins found on the surface of the virus, returning a result within 20 minutes.

But while those systems produce fast results and have received temporary approval by the U.S. Food and Drug Administration, they are somewhat less reliable than another technique called polymerase chain reaction, or PCR, testing, which is considered the gold standard for detecting the virus even though it is a more expensive and laborious process.

Antigen tests can generally detect between 80 and 90 percent of positive cases of COVID-19, the disease caused by the virus, while PCR tests can generally detect between 95 and 98 percent of them, according to the American Health Care Association.

The Trump administration has included three Maine nursing homes on its initial list of facilities to receive the antigen testing machines: Marshwood Center in Lewiston and Seal Rock Health Care in Saco, which have both experienced coronavirus outbreaks, and Coastal Manor in Yarmouth.

It eventually plans to provide those machines to all nursing homes, but has prioritized facilities that are in communities deemed to be “hotspots” of COVID-19, the disease caused by the virus, according to the U.S. Department of Health and Human Services.

Federal officials have said the initiative will help to boost testing in nursing homes, where elderly residents are exceptionally vulnerable to the damaging health effects of the virus and where contagions can swiftly circulate if they are not detected early. Nursing home outbreaks have accounted for a large portion of Maine’s coronavirus deaths.

“Access to rapid point-of-care testing in nursing homes will further protect our nation’s most vulnerable patients,” said Adm. Brett Giroir, assistant secretary for health at the federal agency.

Dr. Jabbar Fazeli, who helps oversee the medical care in a few southern Maine long-term care facilities and is spokesperson for the Maine Medical Directors Association, expressed concern about the use of antigen testing in nursing homes, given their relative inaccuracy and the risk that outbreaks can quickly develop before residents or staff show any symptoms.

Given the nationwide lack of COVID-19 testing resources, he has advocated for facilities to try to administer PCR tests in a strategic way when staff and residents show the slightest possible symptoms of the disease. By relying on antigen tests, he said facilities could receive false negative results that make it harder to detect a nascent outbreak.

“If there are cases in the community, there will be cases in nursing homes, but we need to detect them early in their asymptomatic phase, not when symptoms have already developed,” he said. “With this approach of having a lot of testing, but they’re not very accurate, we would have a lot of tests, but we’d be missing a lot more cases.”

But Maine health officials have said there is some value in antigen testing — so long as they are backed up by PCR tests — and that they will provide appropriate guidance on using them to the state’s long-term care facilities.

They have said that the technology is useful at identifying positive cases of COVID-19 in people who are already showing symptoms, but less accurate at detecting the disease in infected people who do not show symptoms.

The technology also recently produced a set of false positive results at a Maine summer camp that was using it as a precaution on its staff and campers — an approach that the Maine Center for Disease Control and Prevention does not endorse.

Nirav Shah, director of the Maine CDC, said on Tuesday that he would advise nursing homes that a positive result from an antigen test is “pretty accurate” when used on someone with symptoms. But if someone with symptoms tested negative on an antigen test, he would advise that an additional PCR test be done in consultation with the Maine CDC.

“What we know about COVID-19, especially in vulnerable populations like in nursing homes, is that every minute of exposure matters, and so, if you can take somebody out of the milieu because they’ve got a positive and limit their interaction with the staff members or other residents, you’ve got that much better of a shot at preventing one case from turning into 20,” Shah said.

“Are the tests perfect? Certainly not,” Shah added. “But they are a very good start and can shave hours and hours off the process, because in situations like that, every minute counts.”