A cruise ship sits in a dock at dusk.
Enlarge / YOKOHAMA, JAPAN – FEBRUARY 10, 2020: The Diamond Princess cruise ship sits docked at Daikoku Pier where it is being resupplied and newly diagnosed coronavirus cases taken for treatment as it remains in quarantine after a number of the 3,700 people on board were diagnosed with coronavirus.

Japanese health officials on Monday confirmed an additional 65 cases of 2019 novel coronavirus (2019-nCoV) infections aboard the quarantined luxury cruise ship, Diamond Princess, bringing the ship’s case total to 135.

So far, officials have reportedly only tested 439 of the 3,711 passengers and crew members initially aboard the vessel, which has been docked in Yokohama, south of Tokyo, since February 3. People who have tested positive have been removed from the ship and transferred to local hospitals for treatments.

Health officials are now weighing whether they should—and can—test more people. According to The Wall Street Journal, Japan’s health minister, Katsunobu Kato, said that the government has had to reserve testing kits for potential outbreaks in the rest of the country. He also warned that additional testing could potentially delay the end of the quarantine, which for now is set at February 19.

So far, testing has focused on people with symptoms or those who are known to have had contact with the passenger first identified to be sickened with the novel coronavirus—a man from Hong Kong. The man had sailed a five-day leg of the ship’s 14-day roundtrip journey from Yokohama. He disembarked on January 25 in Hong Kong, where he tested positive for the coronavirus ON February 1.

Upon identification of the case, the ship returned to Yokohama on February 3, a day earlier than planned, and has since been quarantined. Passengers have been in isolation in their cabins.

The selective testing and the rising case count have shaken many confined passengers, according to reporting from the Journal. Testing everyone would have “eliminated a lot of anxiety. It would’ve eliminated the question mark,” passenger Kimberly Vincent, a 73-year-old American who lives in Australia, told the outlet. “Some people have been taken to hospitals because of stress, some with heart attacks,” she added.

It’s still unclear how the virus boarded and spread through the ship—whether the first identified case in the man from Hong Kong was the source of other infections and/or whether other passengers brought the virus aboard. Earlier reports indicated that the Hong Kong man’s family, who traveled with him, had not been sickened.

Meanwhile, the outbreak in China continues to rage. There are now over 40,500 confirmed cases worldwide, with 910 deaths. Most of those cases and all but one death occurred in China. Over 300 cases have been reported in around two dozen other countries.