DALIAN, Jan. 3 (Xinhua) -- Preliminary investigation has traced the source of the latest local transmissions of COVID-19 in the northeastern Chinese port city of Dalian to imported cold-chain food, a local health official said Sunday.

Zhao Lian, deputy director of the Dalian municipal health commission, told a press briefing that most of the recent cases reported in the city were related to five dockworkers who got infected by unloading bulk goods from a Russian ship tainted by the novel coronavirus.

The disease control and prevention centers at the national, provincial and municipal levels have conducted whole-genome sequencing of the virus from the confirmed cases, asymptomatic cases, and related environment and goods samples, Zhao said.

The genome sequencing found that the virus strain behind the latest infections in the city was not the same as those found in the city and other parts of the country before and thus ruled out continued local transmissions.

The strain, however, was highly similar to the one found in the imported cold-chain products and also the one prevalent in Russia in November, the official said.

Local health authorities have confirmed the infection source of 75 infections and are tracing the source of three new infections.

The latest outbreak in Dalian was uncovered after several people were found positive for coronavirus after taking routine nucleic acid tests. Authorities found more cases after screening their close contacts and all residents in key areas.