QINGDAO, Dec. 1 (Xinhua) -- One asymptomatic case of COVID-19 was found during regular checks on cold-chain workers in the city of Jiaozhou in east China's Shandong Province, local authorities said Tuesday.

The carrier surnamed Li, 30, is a loader who was also involved in disinfection work at Qingdao Gain Seafood Co. Ltd., according to the municipal health commission of Qingdao, which administers Jiaozhou.

As a cold-chain worker, Li had been undergoing regular COVID-19 nucleic acid tests according to prevention rules and was found positive on Monday.

Packaging samples of a batch of frozen seafood Li had loaded tested positive. The products have been sealed.

So far, health authorities in Qingdao have found 486 close contacts of Li, and they have been quarantined for medical observation and tested for COVID-19. A total of 478 of the contacts are negative and results of the rest are unknown yet.

Qingdao is screening, quarantining, and testing personnel, sealing and disinfecting areas, and conducting further investigations to find people with infection risks.