One hundred forty-eight crew members—out of 632 total—on board the Italian cruise ship Costa Atlantica have tested positive for the novel coronavirus, USA Today reported on Monday.

Cruise ships have proven to be particularly fertile grounds for the coronavirus; cramped, indoor quarantine conditions can contribute to rapid spread. The Centers for Disease Control and Prevention said in March that it had detected traces of the virus on board the Diamond Princess, which was put in quarantine in an outbreak that eventually grew to 712 confirmed cases and 13 deaths, some 17 days after the last people left. That did not necessarily indicate the ship was still infectious, but cleaning cruise liners can be a lengthy and arduous process involving hundreds of workers and weeks of round-the-clock work. Such vessels in the U.S. are currently under an extended no-sail order from the CDC, which has harshly criticized the industry’s handling of outbreaks.

The Costa Atlantica has been docked in Nagasaki, Japan, for scheduled maintenance since late January, and there are no passengers onboard. Costa Cruises told USA Today that all crew are currently bunked in single-occupancy cabins and that employees delivering food and medical supplies are required to wear personal protective equipment. Efforts are reportedly underway to repatriate members of the crew who have tested negative for the virus.

“The health and safety of our people, along with compliance and environmental protection, is always our utmost priority, and we have been constantly monitoring the health of our colleagues on board during the ships’ stay in Japan,” spokesperson Roger Frizzell told the paper.

The outbreak was confirmed last week, when Nagasaki health officials and repair contractor Mitsubishi Heavy Industry said a crew member had shown symptoms. According to Barron’s, on Saturday alone some 58 additional crew members also tested positive.

Japan has around 13,400 confirmed cases of the virus, as well as over 350 deaths. However, very few cases have been confirmed in Nagasaki when excluding those on the docked ship. Reuters reported last week that the official tally in the city stood at just 17 cases and one death.