The recent asymptomatic COVID-19 case in Jiaozhou, a county-level city in Qingdao, was caused by infected cold-chain food and experts have eliminated the possibility of community-level spread, a local health official said on Friday citing scientific evidence.

A worker tested positive for coronavirus on Nov 30 when the city of Jiaozhou carried out routine nucleic acid testing in a local aquatic products company. Later, a roommate of the worker also tested positive.

Kou Zengqiang, who works at the Shandong Provincial Center for Disease Control and Prevention, said a total of 2,521 people who were believed to have contact with asymptomatic coronavirus cases were tested.

"Several rounds of testing have been given to the close contacts or the close contacts' close contacts," Kou said at a news conference held by the province's information office Friday.

"To date, all results came out negative," Kou said.

Epidemiologists tested 4,612 samples from all 22 batches of goods since the beginning of October in the company, and four samples tested positive.

Evidence showed the worker carried those infected goods from Oct 25 to Nov 30, Kou said.

Epidemiologists also found the genome sequences of the samples taken from the goods and the worker were 100 percent identical, strongly suggesting the epidemic started with contaminated goods, Kou added.