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 amid regional outbreaks and ahead of the Lunar New Year holidays.

A throat swab on a 52-year-old man in Weinan, a city in northern Shaanxi province, showed negative results after the person showed symptoms such as coughing and appetite loss, a city official said on Wednesday, but he tested positive using nose and anal swabs...