Officials took anal swabs from residents of neighbourhoods with confirmed Covid-19 cases in Beijing last week, according to the state broadcaster CCTV, while those in designated quarantine facilities have also had the tests.

Small, localised outbreaks in recent weeks have resulted in multiple cities in northern China being sealed off from the rest of the country and prompted mass testing campaigns, which had mostly been conducted using throat and nose swabs.

The anal swabs method “can increase the detection rate of infected people” as traces of the virus linger longer in the anus than in the respiratory tract, Li Tongzeng, a senior doctor from Beijing’s Youan hospital, told CCTV.