Study shows virus traces in faecal samples could remain detectable for a longer time and provide more accurate test results.

Some Chinese cities are using samples taken from the anus to detect potential COVID-19 infections as China steps up screening to make sure no potential carrier of the new coronavirus is missed ahead of next month’s the Lunar New Year holidays when tens of millions of people usually travel home to their families.

China has been battling new pockets of the disease that have appeared in the north and northeast with strict lockdowns and mass testing in a bid to stamp out the outbreaks.

Justifying the decision to take anal swabs, a city official in Weinan in northern Shaanxi province said a 52-year-old man with symptoms including coughing initially tested negative for COVID-19. He was then tested via an anal swab.

The man, who was confined to a centralised facility for medical observation as a close contact of another COVID-19 patient earlier this month, was then confirmed to have the virus, the official told a news conference.

Anal swabs require inserting a cotton swab three to five centimetres (1.2 to two inches) into the anus and gently rotating it.

In a video posted online by state-backed newspaper Global Times, Zhang Wenhong of Huashan Hospital in Shanghai, said that such swabs could be useful in helping minimise the risk of a relapse after recovery.

“There may be traces of the coronavirus detected in the abdominal cavity faeces and intestine,” Zhang was quoted as saying in the report.

Last week, a Beijing city official said that anal swabs were taken from more than 1,000 teachers, staffers and students at a primary school in the city after an infection had been found there. Nose and throat swabs and serum samples were also collected for testing.

Additional tests using anal swabs can pick up infections that other tests miss, as virus traces in faecal samples or anal swabs could remain detectable for a longer time than in samples taken from upper respiratory tract, Dr Li Tongzeng, a respiratory and infectious disease specialist in Beijing city, told state TV last week.

Li added that such samples were only necessarily for key groups such as those under quarantine.

‘Low harm, extreme humiliation’

Stool tests may be more effective than respiratory tests in identifying COVID-19 infections in children and infants since they carry a higher viral load in their stool than adults, researchers at the Chinese University of Hong Kong (CUHK) found in a paper published last year.

Users of China’s Weibo, its Twitter-like social media platform, reacted to the method with a mix of mirth and horror.

“So lucky I returned to China earlier,” one user wrote.

“Low harm, but extreme humiliation,” another said, using a laughing emoticon.

Others who had undergone the procedure chimed in with dark humour.

“I’ve done two anal swabs, every time I did one I had to do a throat swab afterwards – I was so scared the nurse would forget to use a new swab,” one Weibo user joked.