Limited Space Hinders Infection Control on Cruise Ships, Experts Say

A voyage that promised dreams turned into a nightmare when three passengers died from hantavirus and others showed symptoms on the Atlantic expedition of the MV Hondius.

An outbreak of norovirus is under investigation on another cruise ship, while flu, E. coli and varicella have also caused problems in such settings.

In 2020, the Diamond Princess became a breeding ground for COVID-19, with over 700 of the 3,711 people onboard testing positive after a two-week quarantine off Japan’s coast.

Cruise ships can become hotbeds of infection because they are floating behemoths where people interact frequently at close quarters, and passengers come from different countries with varying immunity levels, researchers note.

“Which means you have people potentially in contact with pathogens that they don’t encounter on the day to day,” said Dr. Charlotte Hammer, an infectious diseases epidemiologist at the University of Cambridge.

A substantial proportion of passengers tend to be older adults, who may be more susceptible to certain diseases, setting the stage for potential disaster.

“Whether or not [outbreaks] begin on a ship depends on who comes onboard, if any people are infected when they come onboard, and with which pathogen they might be infected,” said David Heymann, a professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine.

Infections can be transmitted via respiratory aerosols or droplets that contaminate surfaces, as with COVID-19 and flu, or through contaminated food and water systems.

While many ships have improved ventilation, Hammer noted limits: “You’re not going to have high ceilings on a boat. You are not going to have the airflow of two open windows, just because most cabins do not have windows. So there is, in terms of the sheer engineering of a ship, only so much you can do.”

Contaminated food often causes E. coli and norovirus outbreaks; cruise ship kitchens, while hygienic, are a single point of failure. “Again, that is sort of the core engineering. You can’t have X number of backup kitchens on a ship because you only have so much space,” Hammer said.

Dr. Vikram Niranjan, an assistant professor in public health at the University of Limerick, said buffets are potential spread points because everyone shares serving utensils. “Ships aren’t dirty, they are just efficient mixing chambers,” he said.

Water system outbreaks, such as Legionnaires’ disease, are difficult to identify and manage, Heymann noted: “That’s very difficult to deal with. 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, diagnosis is challenging. Hantavirus is rare, and medical teams may not immediately recognize it. “You would begin to suspect if a lot of people had it. But if you saw just one hantavirus infection, it looks like any other viral infection,” Heymann said.

Ships lack full laboratories and hospital equipment, Hammer said: “You have limitations in terms of testing, particularly for something that’s a bit rarer. You have limitations in terms of medical space, medical professionals.”

Niranjan said cruise ships often have isolation space and ventilators but are not prepared for mass outbreaks, suggesting collapsible isolation cabins as a potential solution.

Heymann recommended better training for ship doctors: “Hopefully, these doctors will begin to get more skills in epidemiology and in dealing with outbreaks so that when an outbreak does occur on a ship, they can minimise the transmission.”

Passengers can take precautions including not boarding if ill, regular handwashing, vaccination, travel insurance, and packing face masks, according to guidance from the U.S. Centers for Disease Control and Prevention and Niranjan. Hammer added that many outbreak risk factors are hard to change without altering the cruise ship experience itself: “You can make it not move any more – but that sort of defeats the point.”