A medical worker collects a swab sample from a child at a community in Yuhua District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. (Xinhua/Jin Haoyuan)

A medical worker collects a swab sample from a resident at a community in Yuhua District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. (Xinhua/Jin Haoyuan)

Community staff register for a resident at a community in Qiaoxi District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. (Xinhua/Jin Haoyuan)

Medical workers seal a sample at a community in Yuhua District of Shijiazhuang, capital of north China's Hebei Province, Jan. 7, 2021. Shijiazhuang started to conduct citywide nucleic acid tests covering all residents on Wednesday. (Xinhua/Jin Haoyuan)