‘You only have so much space’: the limits of reducing infection risk on cruise ships | Infectious diseases

IIt was a voyage that promised things one could only dream of, but within weeks the MV Hondius’ Atlantic expedition had become a nightmare, with three passengers dying from the hantavirus and others showing symptoms.

Meanwhile, a norovirus outbreak is under investigation on another cruise ship, while the flu, E.coli and chickenpox – the virus that causes chickenpox – have also caused problems in such settings. Perhaps most memorably, in 2020 the Diamond Princess became a breeding ground for Covid, with passengers and crew quarantined for two weeks off the coast of Japan and more than 700 of the 3,711 people on board ultimately testing positive.

In some ways, it’s hardly surprising that cruise ships can become hotbeds of infection: many of them are floating giants where people on board interact frequently and closely. The researchers also note that many of the people on board will be from different countries, have traveled to different locations, and will have varying degrees of immunity to disease.

Additionally, the ship is moving. “Which means you have people potentially coming into contact with pathogens that they don’t encounter on a daily basis,” says Dr Charlotte Hammer, an infectious disease epidemiologist at the University of Cambridge.

Add to this that a significant proportion of passengers tend to be elderly, who may be more susceptible to certain illnesses, and the stage seems set for potential disaster.

David Heymann, professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine, says: “Whether or not [outbreaks] starting aboard a ship depends on who gets on board, whether people are infected when they arrive on board, and what pathogen they might be infected with.

As Heymann points out, infections can be transmitted in different ways. The first is respiratory transmission between people, either via aerosols – tiny particles that linger in the air and can be inhaled – or via droplets that can either fall directly on people or contaminate surfaces. Covid and the flu are among the diseases that are spread this way.

While many ships have made efforts to improve their ventilation to improve air quality, Hammer notes that there are limits to what can be done. “You won’t have high ceilings on a boat. You won’t have the airflow of two open windows, simply because most cabins don’t have windows,” she says. “So in terms of pure engineering of a ship, there’s not much you can do.”

Another way that diseases can spread is through contaminated food, as is often the case with E.coli and norovirus outbreaks. Hammer says a key issue on cruise ships is that while their galleys offer high levels of hygiene, they are also a single point of failure. “Again, it’s kind of basic engineering. You can’t have X number of emergency galleys on a ship because you only have so many spaces.”

Dr Vikram Niranjan, assistant professor of public health at the University of Limerick, says buffets are a potential point of spread, particularly because everyone shares the same serving utensils. And there are other surfaces that are touched regularly. “The vessels are not dirty, they are simply efficient mixing chambers,” he says.

There is also the possibility of outbreaks spreading through water systems. Cruise ships have previously experienced outbreaks of Legionnaires’ disease, a lung infection caused by inhaling water droplets containing Legionella. “It’s very difficult to deal with,” Heymann says. “First of all, you have to show that the organism is in the water, and the ship may not have the means to do that.”

Once an outbreak begins, cruise ships face challenges, including diagnostics. Hantavirus, for example, is rare and only one strain is known to spread from person to person. As a result, the medical team on board – which sometimes includes only one doctor – does not immediately realize what they are facing. “You would start to suspect it if a lot of people had it. But if you only saw one hantavirus infection, it looks like any other viral infection,” says Heymann.

As Hammer notes, the ships do not have full laboratories or a full complement of hospital equipment. “There are limitations in terms of testing, especially for something a little rarer,” she says. “You have limitations in terms of medical space, medical professionals.”

Niranjan says that while cruise ships often have isolation space and ventilators, they are not prepared for mass outbreaks. He says one option could be to have collapsible isolation cabins that can be used in an emergency.

Heymann says another change that could be made would be for larger cruise ships to ensure their doctors are better trained for such scenarios. “Hopefully, these doctors will begin to acquire more skills in epidemiology and outbreak management so that when an outbreak occurs on board a ship, they can minimize transmission. »

Passengers can take precautions. The U.S. Centers for Disease Control and Prevention has issued guidelines emphasizing not boarding if sick, washing your hands regularly on board, getting vaccinated against common illnesses, receiving destination-specific vaccines or medications, and notifying the ship’s medical center if you are ill. He also mentions the importance of having travel insurance. Niranjan adds that it might be worth bringing masks.

Hammer says many of the factors that put cruise ships at risk of outbreaks aren’t necessarily easy to change. “Or rather, if you change them, the cruise ship is no longer a cruise ship,” she says. “You can stop it from moving, but that defeats the purpose.”