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The outbreak of COVID-19 at a restaurant in the southern Chinese city of Guangzhou was a puzzle.

The suspected index patient was a visitor from the coronavirus’s epicentre in Wuhan. But the eight other customers who later tested positive were not sitting close enough for regular droplet transmission, and most of the patrons and staff avoided infection altogether.

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A team of local scientists eventually came to an eye-opening conclusion about the episode: virus-containing particles had hitched a ride on currents created by the eatery’s air-conditioning.

The prevailing view is that the novel coronavirus is transmitted only by close contact with relatively heavy droplets. But for a group of mechanical engineers at the University of Alberta, the finding was no surprise. In their world, they say, it’s well known that building ventilation systems are efficient disseminators of viruses and other pathogens, and they believe the COVID-19 bug is no exception.