China has begun testing people it considers as high risk for contracting COVID-19 with anal swabs amid a new outbreak, Newsweek reported Tuesday, saying that more than a million Beijing residents have undergone such a test. Local experts are reported as saying the rectal method is more accurate than the commonplace nasal test.

Public health authorities in Beijing said they were seeking to screen over 2 million people in 48 hours, according to the publication. Of those people, about 1.6 million Daxing residents were to be given antibody tests in addition to the throat, nasal, and rectal nucleic acid swabs.

Notably, the publication reported that anal swabs have been used since last year—but for those living in coronavirus hotspots such as Shanghai, according to an infectious disease expert quoted by China’s state broadcaster CCTV on Saturday.

“Since the start of the coronavirus outbreak, we’ve tested for the virus using mainly throat swabs. Its characteristics are convenience and speed, so it’s suitable for large-scale testing,” Beijing You’an Hospital’s Li Tongzeng said, per Newsweek. “Nasal swabs are more accurate than throat swabs, but nasal swabs can be uncomfortable.”

“In some asymptomatic cases or in individuals with mild symptoms, they tend to recover from the illness very quickly,” he added. “It’s possible that there will be no trace of the virus in their throat after three to five days.

“What we’ve found is that in some infected patients, the coronavirus survives for a longer period of time in their digestive tract or excrement than in their respiratory tract,” Li also said.

The anal swabs are meant to be inserted 3 to 5 centimeters (1.2 to 2 inches) up the patient’s rectum, according to guidelines published by China’s National Health Commission, per Newsweek.

On Sunday, CCTV said that anal swabs would not be used as widely as other methods, saying the method was “not convenient,” according to The Guardian.

Li also said that anal swabs boost the COVID-19 detectability rate and decrease the likelihood of false positives.

“Of course, anal swabs aren’t as convenient as throat swabs, so they’re only being used on individuals in key quarantine areas,” Li added, per Newsweek. “This will reduce the return of false positives.”

This reporter reached out to the White House and to the Centers for Disease Control and Prevention (CDC) for comment about these rectal tests but received no response.

You can follow Douglas Braff on Twitter @Douglas_P_Braff.