The National Health Commission (NHC) Saturday reiterated that the major transmission routes of the new coronavirus are still respiratory droplets and contact, and other routes such as aerosol transmission and fecal-oral transmission remain to be confirmed.  

The statement, published in the "Question and Answer" section of the NHC's website, came amid speculation about the possible transmission of the deadly coronavirus through aerosols, or smaller particles that can travel a longer distance than droplets from a patient's sneezing or coughing.  

Aerosol transmission refers to when the respiratory droplets lose water in the air, and the leftover proteins and pathogens form nuclei or dust floats far away in the form of aerosols, causing long-distance transmissions, the NHC said, citing Feng Luzhao, a researcher at the Department of Infectious Diseases at the Chinese Center for Disease Control and Prevention. 

"There is no proof of novel coronavirus transmission through aerosols so far," it added.  

"Epidemiological investigations have shown that most of the confirmed cases used to have close contact with infected patients," the commission said.  

The conclusion is written in the fifth edition of the diagnosis and treatment program of the coronavirus published by the NHC on Sunday morning. 

Aerosol transmission can only occur under certain special conditions, such as when performing medical procedures, according to Feng.  

Asked whether the novel coronavirus is in the air, the commission said that as the virus mainly transmits through droplets, which can't spread long, there is generally no novel coronavirus in the air at places with normal ventilation.  

Therefore, residents are recommended to open the windows at least twice a day, which is an effective measure to reduce the risk of infection, it said.  

The World Health Organization (WHO) was also asked about whether the novel coronavirus could be transmitted through aerosols. In its response on Saturday, WHO did not confirm, but said the evidence shows that the virus is transmitted by droplets, which are heavier and hard to float in the air. 

However, this is a new virus, WHO said, adding it will continue to monitor any possible means of transmission. 

Online posts about possible transmission routes through aerosols have been circulating in social media recently as the new virus killed hundreds of people in China and infected more than 30,000 people.  

The fear was reignited on Saturday when Zeng Qun, deputy head of the Shanghai Civil Affairs Bureau, said at a press conference that aerosol transmission was confirmed.