A woman wearing a face mask is seen on a bus amid the novel coronavirus outbreak in Tehran, Iran, on March 2, 2020.(Photo by Ahmad Halabisaz/Xinhua)

 A recent case study of a dozen passengers infected with COVID-19 after taking a bus suggested that the coronavirus can survive at least 30 minutes and transmit 4.5 meters in a closed air-conditioned environment, triggering concerns over safety of public transportation. 

The research paper, co-authored by medical staff members of the Chinese Centers for Disease Control (CDC) Luo Kaiwei, Hai Zheng and others, was published on Thursday, Shanghai-based media outlet The Paper reported on Sunday.

The research paper looked into the possibility of transmission of the aerosol in a closed environment. 

The paper introduced a case of a cluster of infections in Hunan Province in which a passenger, or Patient A, was not wearing a face mask and infected eight other people in an air-conditioned bus on January 22. Patient A was confirmed to have contracted the virus on January 28. 

Also on January 22, Patient A took another air-conditioned shuttle bus for about one hour and infected two more people.

The eleventh infection was a passenger who took the shuttle bus half an hour after Patient A got off the bus, which suggested that the virus can effectively survive in a closed air-conditioned environment for at least 30 minutes and cause human disease, said the paper.

Two of the passengers infected by Patient A went on to infect their relatives.

The distance between Patient A and the nearest infected passenger in the bus was less than 0.5 meters, and the farthest about 4.5 meters.

Patient A and the farthest infected passenger did not have close contact on the way. Most of the passengers were not wearing face masks.

A total of 243 close contacts were identified in the case, with 13 confirmed infections.

The long-distance transmission in this case also raises the possibility of aerosol transmission of the coronavirus in a closed environment, the study said. In addition, the study noted that the transmission distance of the virus in an air-conditioned environment could exceed the commonly recognized range of 1 to 2 meters.

The case study triggered concerns among the Chinese public, with many netizens worried about their safety when taking public transport for work. 

According to the fifth version of the prevention and control plan of the coronavirus published by China's National Health Commission on February 21, the virus' main routes of transmission are respiratory droplets and contact transmission, and prolonged exposure to high concentrations of aerosol in a relatively closed environment can also spread the virus. Other routes of transmission have yet to be identified, the document noted.

Global Times