The National Health Commission reiterated on Sunday that the transmission routes of the novel coronavirus through aerosols and digestive tracts have yet to be confirmed.

"So far, we've made clear that the transmission routes of the novel coronavirus are through droplets and contacts, and the other transmission routes, such as through aerosol and fecal-oral, need to be further clarified," the commission said during a media briefing.

In a post on its WeChat account on Sunday it said, "Most confirmed cases of the novel coronavirus pneumonia can be traced to close contact with previously confirmed patients, according to our epidemiological investigations."

In the fifth edition of the diagnosis and treatment plans for NCP, released on Saturday, the commission said the transmission routes of the virus through aerosols and digestive tracts had not been identified.

Experts explained that aerosols refer to liquid or small particles suspended in the air. People exhale aerosols all the time, from breathing and talking to singing and sneezing.

They added that the diameter of droplets produced by talking or sneezing is usually more than 1 millimeter while that of aerosols is less than 0.1 mm.

"Being much smaller, aerosols won't drop to the surface of something or to the ground immediately. Instead, they will linger in the air for as long as several days," said Wang Minghuai, a professor from the School of Atmospheric Sciences at Nanjing University in Jiangsu province.

Doctors said that many viruses causing respiratory diseases are transmitted via aerosols, but that such transmission happens only rarely in open areas as there are various substances in the air, including ultraviolet rays and free radicals with strong oxidation properties that will largely reduce the toxicity, while their density is naturally diluted in the air.

So people will only get infected by a virus through aerosol transmission when they enter an enclosed space, such as an elevator recently vacated by an infected person who coughed a lot, doctors said. They reminded people to wear face masks at all times in public places and to avoid poorly ventilated places as much as possible.

Cao Junji, director of the Chinese Academy of Sciences' Key Laboratory of Aerosol Chemistry and Physics, reminded people to maintain ventilation or use air purifiers when at home or in the office to reduce possible virus concentrations in the air.

Shen Yinzhong, director of infectious diseases at the Shanghai Public Health Clinical Center, said the aerosol transmission route posed a greater health threat to front-line medical workers than the general public as the use of some medical devices, including respirators and atomizers, generated aerosols.