The study also recommends that indoor venues should also fit a “wind partition” between customers or put them in separate rooms to reduce infection risk.
Researchers made their findings after examining a cluster of cases at a restaurant in Jeonju, South Korea, earlier this year.
Following scrutiny of CCTV images, contact tracing interviews and mobile phone location data, they found that one patient had been infected at a distance of 6.5 metres despite only being exposed for five minutes.
Another was infected at a distance of 4.8 metres after 15 minutes’ exposure.
Neither had any direct or indirect contact with the original case.
But despite several other diners in the same restaurant being nearer to the source of the outbreak, several other people were not infected.
“Therefore, updated guidelines involving prevention, contact tracing, and quarantine for COVID-19 are required for control of this highly contagious disease.”
The researchers also said diners should avoid talking in the restaurants to reduce risk of infection.