A staff member collects sample for testing at Tongji community in Shulan, northeast China's Jilin Province, May 17, 2020. Jilin Province reported three new confirmed COVID-19 cases on Saturday, local health authorities said Sunday. (Xinhua/Zhang Nan)

A COVID-19 superspreader in Northeast China's Jilin Province, who caused more than 100 people to be infected, was reportedly engaged in a health-related marketing promotion. Experts warned that health seminars targeting elderly people are blind spots in the epidemic prevention and control work in residential communities.

The 45-year-old male surnamed Lin, who was identified as a silent coronavirus carrier on Tuesday, was reported to have become a confirmed case on Sunday. He came from neighboring Heilongjiang Province and has traveled on trains and buses in three cities in Jilin. 

Lin was reported to have given four lectures at two health clubs in Jilin's Gongzhuling and Tonghua as a self-employed marketer from January 8 to 11, causing a total of 118 people to be infected directly and indirectly, including 80 people who attended the lectures or worked in the clubs.

The infected people are mostly middle-aged and elderly. Ten of them are above 80 years old, with the oldest being 93. 

Lin told the media that he was just promoting the sales of linseed oil at the clubs and was not giving any health-related lectures, the Beijing News reported on Monday.

Authorities have carried out a joint investigation into the health clubs that organized Lin's marketing promotions to determine if the clubs' operations or the products being sold were illegal or in violation of local regulations, said an official from the market supervision department of the Jilin government at the press conference. 

Gongzhuling announced on Monday it was rolling out citywide free nucleic acid tests and imposing strict sealed-off management on residential communities, requiring all citizens to quarantine at home, with daily necessities to be brought by community service workers.

Health clubs that regularly hold marketing promotion lectures for elderly people are usually a blind spot in the epidemic prevention and control work in residential communities, which makes it necessary to strengthen the monitoring of this area, as it has a large concentration of elderly people, health experts noted. 

With sporadic cases still occurring in many places, any mass gathering events, especially indoors, are risky, whether it is a health seminar or a conference training session, Wang Peiyu, a deputy head of Peking University's School of Public Health, told the Global Times on Sunday.

Jilin has ordered restrictions on the operations of recreational public venues and mass events in the worst-affected cities, and adjusted the emergency response level to medium in residential communities where infections have occurred.

This superspreading case also prompted other cities to order the suspension of sales activities that involve mass gatherings, such as Fushun in Northeast China's Liaoning Province and Shaoxing in East China's Zhejiang Province. 

Jilin has become one of the provinces in China worst-hit by the current outbreaks, with a total of 34 active confirmed cases and 80 asymptomatic patients as of press time. 

The fresh outbreak in the province started on Monday, and was imported from Wangkui county, the epicenter of Heilongjiang.