Based on a local outbreak case on January 22 during the peak Lunar New Year travel season, the research followed a passenger who boarded a fully booked long-distance bus and sat in the second row from the back.
The passenger, known as “A”, already felt unwell. But China was yet to declare the coronavirus outbreak a national crisis, so the passenger did not wear a mask, nor did the driver or most of the other passengers on the 48-seat bus.
Lead author of the study Hu Shixiong, who works for the Hunan Provincial Centre for Disease Control and Prevention, said security camera footage showed patient “A” did not interact with others throughout the four-hour ride.
Yet, by the time the bus stopped at the next city, the virus had already jumped from “A” to seven other passengers.
These passengers weren’t only sitting relatively close to “patient zero”. Some were six rows – roughly 4.5m – away, and all later tested positive, including one passenger who displayed no symptoms of the disease.
After these passengers left, another group got on the bus about half an hour later.
One passenger sitting in the front row, who was also not wearing a mask, became infected. Mr Hu said this patient was likely to have inhaled the particles breathed out by the infected passengers from the previous group.
“The possible reason is that in a completely enclosed space, the airflow is mainly driven by the hot air generated by the airconditioning. The rise of the hot air can transport the virus-laden droplets to a greater distance,” the scientists noted.
As for patient “A”, after getting off the first bus, they got on a minibus and travelled for another hour, infecting two new passengers.
By the time the study was finished in mid-February, patient “A” had infected at least 13 people.
The scientists said the study proved the importance of washing hands and wearing a mask in a public place despite advice from other health officials that
unless you’re unwell.
“Our advice is to wear a face mask all the way (through the bus ride),” they wrote in the paper, which found that those on-board the bus who
did wear a face mask did not become infected.
“When riding on more closed public transport 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 avoiding touching your face before cleaning.”