The outbreak of coronavirus on a cruise liner now quarantined off Yokohama highlights the high risk of the infection spreading in confined spaces, with health experts warning that the danger is greater on ships, buses and trains than it is on planes.

The deadly pneumonia-causing virus, which can spread through droplets from coughs and sneezes, is more likely to cause infections if passengers are within a 1-meter radius of someone who has symptoms, the experts said.

On airplanes, the risk is lower because the recycled air in the cabins is ventilated through filters designed to remove viruses and germs, and respiratory droplets will fall on the floor as the air flows downward, they said.

“The degree of congestion hugely affects” the risk, said Yasuhiro Kanatani, a Tokai University professor who specializes in public health.

As one example, he said the danger of infection on bus tours is relatively high because passengers are together for a long period.

In late January, a tour guide living in Osaka Prefecture was found to be infected with the new virus, in addition to a Japanese bus driver who was with her and Chinese tourists from the city of Wuhan, the epicenter of the outbreak, for several days.

On Thursday, 10 more people aboard the Diamond Princess cruise ship docked at Yokohama port tested positive for the coronavirus, in addition to the 10 who tested positive a day earlier. The new cases brought Japan’s total number of confirmed infections to 45.

One person aboard the Diamond Princess said passengers were allowed to freely move around the ship, which is equipped with amenities including a casino, theater, fitness center and sauna. The passenger said they were allowed to dine at restaurants until Tuesday but that meals were switched to room delivery from Wednesday morning.

The passengers and crew from 56 countries and regions will be quarantined aboard the ship for 14 days.

On cruise ships, group infections of influenza and norovirus have been reported in the past, said Reiko Saito, a Niigata University professor.

“There has been a case in which a third of crew members were infected with influenza,” she said.

As for measures to prevent viral infections on trains and buses, health experts have advised people to commute during off-peak hours and take advantage of remote work if they can.

They added that those who have a cough and are sneezing should wear masks.

Tokai University’s Kanatani stressed that people should not carelessly touch their nose, mouth or eyes after getting off public transportation. The health ministry is also urging thorough alcohol disinfection.

RELATED PHOTOS The cruise ship Diamond Princess approaches Yokohama port Thursday morning. Ten more people on the ship have tested positive for the coronavirus. | REUTERS