A study from a group of official researchers from Hunan province found that the respiratory droplets of coronavirus (Covid-19) can linger in the air for at least 30 minutes and travel up to 4.5 metres.
The findings challenged the advice from the health authorities around the world saying that people should stay apart at a “safe distance” of one to two metres to avoid contracting the virus.
According to the study, the coronavirus droplets, which can last for days on surfaces, have different lingering time based on factors such as temperature and the type of surface. For example, the virus can last for two to three days on glass, fabric, metal, plastic, or paper at around 37°c.
If an unsuspecting person touches the surface and then rubs their face and hands, the risk of transmission is higher, the study said while adding that the virus could survive more than five days in human faeces or bodily fluids.
Highlighting that the virus can linger in the air and attach to fine droplets or particles, the study also acknowledged that washing hands and wearing a mask in public place is important.
The researchers published the paper in peer-review journal Practical Preventive Medicine last Friday (6 March) based on the study on a local outbreak case of coronavirus on 22 Jan during the peak Lunar New Year travel season, reported by South China Morning Post (SCMP).
Researchers explain how the virus is transmitted
The researchers said that the outbreak case involved a patient zero who had infected 13 passengers while travelling on a fully booked long-distance 48-seater bus.
Noting that the outbreak case happened before China declared the coronavirus as a national crisis, patient zero, who was already sick did not wear a mask, nor did most of the other passengers and driver on the bus.
Based on the security camera footage installed in the bus where windows were all closed, the study’s lead author who works for the Hunan Provincial Centre for Diseases Control and Prevention, Hu Shixong, said that patient zero sat on the second row from the back and did not have any interaction with other passengers throughout the four-hour ride.
However, before the bus stopped at the next city, the virus had already transmitted from patient zero to seven other passengers, who all later tested positive for the coronavirus, including one passenger who did not display any symptoms.
The infected passengers included people who sat relatively close to the patient as well as a couple of passengers sitting six rows away – about 4.5 metres away from the patient.
A passenger who boarded the bus 30 minutes after these passengers got off from the bus was also infected with the coronavirus. As explained by Mr Hu, this passenger who did not wear a mask could have inhaled aerosols or tiny particles exhaled out by the infected passengers from the previous group.
At the same time, patient zero later boarded a minibus and travelled for another hour, infecting two more passengers sitting 4.5 metres away from him.
From the case study, the researchers cautioned that the virus could remain afloat even after the carrier has left the bus.
“It can be confirmed that in a closed environment with air-conditioning, the transmission distance of the new coronavirus will exceed the commonly recognised safe distance,” the researchers wrote in the paper.
They added, “The possible reason is that in a completely enclosed space, the airflow is mainly driven by the hot air generated by the air conditioning. The rise of the hot air can transport the virus-laden droplets to a greater distance.”
People should wear face mask all the time in public, said researchers
Despite the transmission distance, the researchers also advised people to wear a face mask all the way as they discovered that the passengers in the two buses who wore a face mask were not infected with the coronavirus.
They remarked, “When riding on more closed public transportation such as subways, cars, planes, etc, you should wear a mask all the time, and at the same time, minimise the contact between your hands and public areas, and avoid touching your face before cleaning.”
The sanitation on public transport should be improved, such as cleaning and disinfecting the interiors once or twice a day, especially after passengers arrive at the terminal, said the researchers.
The researchers also suggested adjusting the air conditioning to maximise the volume of fresh air supplied in public transport.
However, there is also uncertainty in this study where passengers who sit immediately next to patient zero were not infected with coronavirus though they have a higher risk of exposure to the virus in the air.
Doubting the credibility of the study, a doctor in Beijing involved in diagnosing and treating Covid-19 patients told SCMP that some questions have not been answered in the study. He added, “Our knowledge about this virus’s transmission is still limited.”