Fast walking down a narrow corridor could help the coronavirus spread, research suggests.
Experts warned early in the outbreak transmission would be higher in enclosed spaces, encouraging ventilation and outdoor socialising as much as possible.
To better understand the risk, scientists from the American Institute of Physics in Maryland used computer simulations to predict how coronavirus-laden droplets disperse through the air.
Results suggest if a person coughs while walking quickly down a corridor, expelled droplets travel around and behind their body.
A “recirculation bubble” or “tail” then develops directly behind the cougher’s torso, streaming out at approximately waist height.
This could put children – who tend to develop mild coronavirus symptoms or none at all – at particular risk of infection, warned the scientists.
“The flow patterns we found are strongly related to the shape of the human body,” said study author Xiaolei Yang.
“At 2m (6.5ft) downstream, the wake is almost negligible at mouth height and leg height, but is still visible at waist height.”
The same simulation technique has previously helped scientists understand how windows, air conditioners and toilet flushes influence air flow and viral transmission.
Simulations have tended to assume an infected individual is in a large indoor space, failing to account for nearby walls, like in a corridor.
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The American Institute team’s results, published in the journal Physics of Fluids, revealed two virus dispersal modes. It is unclear how they defined fast walking.
In the first, a cloud of droplets detaches from the moving person, floating far behind them to create a bubble of virus-laden droplets.
In the second, the cloud attaches to the person’s back, trailing behind them like a tail as they move.
“For the detached mode, the droplet concentration is much higher than for the attached mode, five seconds after a cough,” said Yang.
“This poses a great challenge in determining a safe social distance in places like a very narrow corridor, where a person may inhale viral droplets even if the patient is far in front of him or her.”
For both modes, the cloud of droplets hovers at around an adult’s waist height, putting it in line with many children’s mouths.
Statistics have repeatedly shown children have a significantly lower risk of coronavirus complications, with research even suggesting they are half as likely to catch the infection in the first place.
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