A medical worker takes a swab sample from a resident.

China has introduced anal swabs, as a new type of test that could detect coronavirus more accurately.

"If we add anal swab testing, it can raise our rate of identifying infected patients," Li Tongzeng, an infectious-disease specialist at Beijing You'an Hospital, said on state-run broadcaster China Central Television Sunday. 

"But of course, considering that collecting anal swabs is not as convenient as throat swabs, at the moment only key groups such as those in quarantine receive both," Tongzeng added.

An anal swab test means inserting a cotton-tipped swab about 3-5cm (1-2 inches) into the rectum, which is then sent to a lab to be tested for the virus. They are analyzed in the same way as the Polymerase Chain Reaction (PCR) coronavirus tests taken from the nose or throat.

Tonzeng said that a study has shown the virus lasts longer in the anus or faeces than in the respiratory tract. So an anal swab or faecal sample could be useful for identifying disease in mild or asymptomatic cases. 

But Yang Zhanqiu, deputy director of the pathogen biology department at Wuhan University, told state-run tabloid, The Global Times, that since the virus has been proven to be contracted via the upper respiratory tract rather than the digestive system, the most efficient tests are still nasal and throat swabs. 

"There have been cases concerning the coronavirus testing positive in a patient's excrement, but no evidence has suggested it had been transmitted through one's digestive system," Yang said. 

Joanne Santini, professor of microbiology at University College London, told Insider anal swabs are not nice way of testing, but it makes sense. "It's the obvious thing to do," Santini said.

Santini explained that the virus attaches to the human body using a receptor called ACE2, and there are many ACE2 receptors in the gut. The viral load - the amount of virus shedded  - can also be higher in the faeces, especially if someone is suffering with gastrointestinal problems caused by coronavirus. And viral shedding can last for longer in the faeces than in sputum.

"Even though a common way of being infected is through respiration, I think there must be some infection happening through the gut via the mouth," she said. "There is evidence that SARS-CoV-2 in faeces is infectious, just like other viruses, such as norovirus and other coronaviruses."

Santini said that poo samples, however, would be preferable to anal swabs because they are less invasive and could be particularly useful for collecting samples in kids.

"It's less painful for kids, and people do it all the time for other tests," she said. "You don't have to go anywhere, and you can do it yourself."

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