After examining CCTV images, contact tracing interviews and mobile phone location data, they concluded that one patient was 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 and neither had any direct or indirect contact with the original case.
Indoor venues should also install a “wind partition” between customers or consider putting them in separate rooms to prevent the spread of infection.
The recommendations were made in a study into a cluster of cases at a restaurant in Jeonju, South Korea, earlier this year.
However several other diners in the same restaurant were not infected despite being nearer to the source of the outbreak.
The researchers also measured the air flow created by air conditioners mounted on the ceiling to see how the virus may have been transmitted over such long distances.
Experts currently recommended that social distancing requires a minimum of between one and two metres to avoid contact with respiratory droplets that are transmitted by sneezing, coughing or speaking.
However in the Korean case the scientists concluded that the droplets may have been carried longer distances because the restaurant was equipped with ceiling-type air conditioners.
“Droplet transmission can occur at a distance greater than 2 m if there is direct air flow from an infected person,” said the authors of the study in the Journal of Korean Medical Science.
“Therefore, updated guidelines involving prevention, contact tracing, and quarantine for Covid-19 are required for control of this highly contagious disease.”
The researchers go on to recommend that tables in indoor restaurants and cafeterias should either be separated by partitions or be placed more than two metres apart.
“In addition, in indoor settings such as restaurants, masks should be removed only during meals and should be worn before and after eating, while conversation during meals and loud talking or shouting should be avoided,” they add.
“In the long term, installation of separate rooms or bulkheads for indoor settings should be considered to prevent transmission of airborne and droplet infectious diseases.”