© Reuters/Kim Kyung-Hoon

Strict quarantine on a coronavirus-stricken cruise ship called the Diamond Princess may have made the situation worse, some experts say.

On the cruise ship, 286 people have tested positive for the new coronavirus as passengers remain confined to their rooms, but crew members eat and sleep in close quarters.

Experts say that passengers should have been quarantined on land, since a crowded cruise ship is "an incubator for viruses."

Japan's Ministry of Health just announced it would allow certain passengers over 80 years old to finish their quarantine off the ship.

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Quarantine efforts on a coronavirus-stricken cruise ship may have actually helped the virus spread, some experts say.

The ship, called Diamond Princess, is carrying about 3,500 passengers and crew. It has been on a 14-day lockdown in the port of Yokohama, Japan, since it was originally scheduled to dock on February 4.

The ship has seen an unprecedented rate of infection, hosting more coronavirus cases than any country besides China. On Saturday, Japan's Health Minister announced another 67 cases onboard, bringing the ship's total number of infections up to 286. One quarantine officer has even tested positive for the virus.

"There is now ample evidence that this [quarantine] is not preventing the spread of cases within the ship and it is also posing a risk of spread within the ship," Tom Inglesby, an infectious-disease expert and director of the Johns Hopkins Center for Health Security, told TIME.

Since the quarantine began, passengers have been confined to their rooms, with meals delivered to their door every day. People who test positive for the virus have been taken off the ship and transported to medical facilities, according the cruise ship company and Japan's Ministry of Health.

The main problem, several experts have said, has been the decision to keep passengers onboard the ship, especially those who have tested negative for the new coronavirus.

"From a virologist's perspective, a cruise ship with a large number of persons on board is more an incubator for viruses rather than a good place for quarantine," Dr. Anne Gatignol, a microbiologist who studies viruses at McGill University, told the Montreal Gazette.

As experts voice concerns over the quarantine's effectiveness, people onboard the ship have expressed fear and unhappiness with the living conditions.

"I can't wrap my head around the fact that I could die from this cruise," Gay Courter, a 75-year-old novelist confined to a cabin on the ship with her husband, told The Wall Street Journal. "I go look outside and there's people in white hazmat suits."

© AP Photo/Eugene Hoshiko

"There are no clear, obvious precedents for what needs to happen," Inglesby said.

Passengers in interior rooms with no windows are allowed to step onto the ship's deck for a few minutes each day, if they wear N95 respirator masks. The face masks are not great at preventing wearers from contracting the coronavirus, but they may help protect others from being exposed. Authorities have advised passengers to keep a 6-foot distance between themselves at all times.

"They've basically trapped a bunch of people in a large container with [the] virus," David Fisman, an epidemiology professor at University of Toronto, told Vox. "So [I'm] assuming 'quarantine' is generating active transmission."

Other experts have shared similar concerns about the high risk of keeping thousands of people in the close, shared confines of the ship. It's unclear if the virus can spread from the surfaces that a sick person has touched. In a letter to Diamond Princess passengers and crew, the CDC said it had no evidence to indicate that the virus could spread through vents.

"Since the infections began in an enclosed space, if this continues, [the number of patients] will steadily increase," Masahiro Kami, head of the Japanese nonprofit Medical Governance Research Institute, told United Press International on Tuesday. "One minor error and I think a person [on board] can become infected."

© Kyodo/via Reuters

Many experts say that passengers who tested negative for the virus should be removed from the ship and finish their quarantine somewhere else. Though people who test negative could still have the virus, this would lower the risk of healthy people contracting it.

"The decision to keep the passengers and crew on the ship is no longer ethical and is wholly inappropriate," Michael Mina, a professor of epidemiology and immunology at Harvard University, tweeted on Monday. "Clearly this has transmitted among them, placing all at unacceptable risk."

Crew members have been particularly at-risk, since they don't have private rooms. At least 10 staff have tested positive for the coronavirus. According to a New York Times report, those infected crew members had eaten in the mess hall alongside their coworkers.

"We all are really scared and tense," Sonali Thakkar, a worker on the cruise ship, told CNN. "There are many places where we all are together, not separated from each other."

John Lynch, an associate professor of infectious diseases at the University of Washington, also expressed concern to The New York Times about the high risk to crew members. But, he added, "we have to remember that quarantines protect those outside the quarantine, not those within."

© Reuters/Kim Kyung-Hoon

Some experts say we don't yet know enough to determine whether or not the quarantine worked. Marion Koopmans, head of the department of virology at Erasmus Medical Center in Rotterdam, Netherlands, posed the question to Vox: "Are these truly new infections acquired after quarantine, or would these people have already acquired [the virus] and it's just the regular incubation period?"

Japan's Heath Ministry has not offered much comment on the rational behind its decisions for the cruise ship's quarantine, but some have pointed out that it's not easy to find last-minute quarantine facilities for 3,500 people. Some experts have other theories.

"The Japanese government is probably valuing stopping the spread of the novel coronavirus to their country more than the higher risk of harm to passengers from this mass cruise ship quarantine," Steven Hoffman, director of the Global Strategy Lab and a professor of global health at York University, told Vox.

Officials started to move in a new direction on Wednesday, when the Japanese Ministry of Health announced some passengers could leave the ship and finish their quarantine on land. The offer applied to passengers over 80 years old who had a windowless cabin room or pre-existing medical conditions. They will have to test negative for the virus before they can leave.

The 14-day quarantine is scheduled to end on February 19. By then, any remaining guests will have been on the ship for about a month.