A Chinese city tested almost 10 million people for COVID-19 in four days following the appearance of a cluster of cases, local authorities said on Thursday.
A total of 13 infections have been discovered since the weekend.
Altogether, 9.94 million samples were collected, of which 7.6 million had been processed by early Thursday.
The cases were all related to a local hospital.
Authorities used sample pooling, meaning they collected residents’ individual samples and then processed 10 of them at once in a single nucleic acid test.
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If the result in a pool turned out positive, all 10 residents would be notified and required to take individual nucleic acid tests, according to Qingdao’s municipal health commission.
People from other cities who had travelled recently to Qingdao were also required by employers or local party committees to take nucleic acid tests.
The Director of the Qingdao municipal health commission, Sui Zhenhua, was suspended because of the virus’ resurgence, Xinhua news agency reported.
Apart from the Qingdao cluster, China has only recorded coronavirus infections imported from abroad in recent weeks.
The country brought the virus’ spread under control with measures such as motion tracking, locking down cities, and entry bans.