Two customers walk out of a shopping mall in Nanjing, East China's Jiangsu Province on February 19. Photo: cnsphotos

Nanjing of East China's Jiangsu Province reported one asymptomatic case of COVID-19 on Thursday, raising concerns over further infections among local residents and another round of suspended classes on campus as the man did not test positive for the coronavirus until 28 days after he returned from the US and had since been teaching in a training center in the city. 

The man, 19, surnamed Zhou, is an instructor at a basketball training institution located in a shopping center in Jianye district of Nanjing, which mainly trains children from the age of 4 right through to 14 years old. The teaching institution has since been temporarily closed, people.cn reported on Thursday.

A resident of Nanjing, surnamed Bai, mother of an 8-year-old pupil, said she felt worried that the tutoring agencies in the city will close again because of the case, as the basketball training center that her son attended had already announced that it would stop class on Thursday morning due to the situation, although they don't have any branch institutions in the aforementioned shopping center.

"Everything just became normal this semester and I thought we could finally take a breath, and not worry about our health," Bai told the Global Times.

The authority in Nanjing said on Thursday that the man arrived at Nanjing Lukou International Airport on August 11 and conducted a 14-day quarantine at a designated hotel. He tested negative in two nucleic acid tests taken during the isolation period and another upon returning to his residence in Jianye district of Nanjing.

However, the following two tests, taken on September 8 and 9, returned positive results. The man was then quickly admitted to Nanjing public health center for medical observation. He showed no symptoms, however, and his CT examination returned a normal result.

The local authority said the nucleic acid tests of his parents and other close contacts are all negative so far. In addition, the environmental samples taken from places where he had visited also returned negative results.