There are clear epidemiological links between all 16 locally transmitted COVID-19 cases in Shanghai, and none of them contracted the virus from an unknown contact, a senior health official said on Jan 27.

"The first three cases reported last Thursday were discovered through proactive efforts, and the following 13 were found within the closed-loop management of the relevant individuals of the cases," Wu Jinglei, director of the Shanghai Municipal Health Commission, said at a municipal press briefing.

Among the 13 cases, 10 were close contacts of the confirmed patients, and the remaining three were found through screening of individuals who had contact with the cases, Wu said.

Of the first three cases reported last Thursday, two are logistics workers from two local hospitals. They tested positive for COVID-19 during a regular screening conducted by the medical institutions. The third was a friend of one of them.

The new case reported on Monday is a resident in downtown Huangpu district and a family member of a case reported last Thursday.

According to the city's health commission, all those who have had close contact with the confirmed cases have been placed under hotel quarantine. The public venues visited by the confirmed cases over the past two weeks, including two residential neighborhoods and a card room, have been disinfected.

Chen Xiaojie, vice-governor of north Shanghai's Baoshan district, said that authorities have been assisting residents from the district's No 1 and No 2 section of Linjiang Xincun residential neighborhood, which was categorized as a medium-risk area on Saturday after a couple was found to be infected.

"Food, drugs, articles for daily life, and trash collecting service are provided in a timely manner to the residents under home quarantine. For some senior and disabled residents who live on their own, neighborhood workers also provide additional help such as delivering three meals to them every day," she said.