The coronavirus spreads through air conditioning on buses, scientists warn after two dozen cases affected a passenger in China.
Twenty-four bus passengers in Zhejiang Province tested positive for the virus after an hour and a half of travel on January 19.
Scientists believe that air conditioning makes virus transmission possible by spreading the virus directly onto buses.
Some air conditioners take air in and out of the open air, while others, called separate units, recirculate the same air as here.
British experts warned last month that such devices should be switched off or used with windows open to prevent the spread of Covid-19.
Offices, cinemas, theaters and other indoor facilities in the UK must have new air conditioning systems to ensure fresh air exhaust.
The latest study, published in JAMA Internal Medicine, was carried out by scientists from the Provincial Centers for Disease Control and Prevention in Zhejiang Province.
They linked an outbreak back to a passenger on a bus in eastern province on January 19, days before China closed down.
Passengers who were on the bus were not socially distant, but some were believed to be wearing face masks.
A total of 68 passengers boarded the bus for one hour and forty minutes to participate in the Buddhist pilgrimage.
Twenty-four passengers tested positive for Covid-19, 18 of whom were suffering from “moderate illness”. The other six had mild or no symptoms.
The passengers seated closest to the original patient were less likely to fall ill than passengers on the other end of the bus.
This suggests that the air conditioner had a role in trapping virus particles and recycling them elsewhere through bus openings.
The outbreak comes because of warnings from British experts that so-called separate air conditioning devices must be turned off or used with the windows open.
Dr. Sean Fitzgerald, a staff member at the Royal Academy of Engineering, said opening windows with air conditioning could be the best way to reduce risk.
In April, researchers accused the air conditioner of spreading the coronavirus to at least nine other diners who ate at a restaurant in Guangzhou, China, in January.
A research paper published in the journal Emerging Infectious Diseases investigates an incident at a restaurant in January in which a family from Wuhan, the city where the Covid-19 pandemic began, arrived.
The researchers said that one of these family members had an asymptomatic case and just two weeks later the patient contracted the virus along with nine other people, including family members and two other groups at a nearby table in the restaurant.
The affected table in the windowless area is about three feet apart, as the authors claim that the most likely cause of this outbreak is droplet transfer.
However, they say that the droplets only stay in the air for a short time and only cover a short distance.
Therefore, they concluded, AC likely continued to spread the virus among the affected masses.