Inappropriate disinfection in the CT room at the Qingdao Chest Hospital led to the new cluster of COVID-19 infections in Qingdao, east China's Shandong Province, a local health official said Friday.
One of the cases involved a dock worker who had earlier tested positive for the virus but developed symptoms only after about 20 days, the city said.
Nearly 10 million residents in Qingdao have now been screened for the coronavirus, officials said yesterday. There was no community transmission, as such.
There was a nationwide concern as thousands of people had visited the tourist city during the National holidays.
Beijing officials announced strict management of global arrivals to the capital, including three tests - before departure, at Chinese customs and after finishing a quarantine period.
The emergence of a new cluster prompted the city to test the entire population, but no new positive cases have been reported from over 10 million tests.
A total of almost 11 million testings were done.
Chinese hospitals are now treating 253 people for COVID-19, with another 381 people being monitored in isolation for having testing positive for the virus without showing symptoms or for being suspected cases.
Wu Zunyou, chief epidemiologist at the Chinese Center for Disease Control and Prevention, said that "priorities for prevention should be on wards in hospitals".
Health Commission Director Sui Zhenhua and Deng Kai, president of Qingdao's thoracic hospital to which the cases have been linked, have been placed under investigation in connection with the outbreak.
On Sept. 24, Qingdao reported that two dock workers tested positive for the coronavirus during a routine health check, but neither showed any symptoms.
By the end of Thursday, 240 people, who came from overseas were being treated in hospitals. Both of them were asymptomatic, the official said.
The total number of confirmed coronavirus cases in mainland China stands at 85,622, with 4,634 deaths.