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

It was a voyage that promised such stuff as dreams are made of, yet within weeks the Atlantic expedition of the MV Hondius had become a nightmare, with three passengers dead from hantavirus and more showing symptoms. Meanwhile, an outbreak of norovirus is under investigation on another cruise ship, while flu, E coli and varicella – 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 onboard eventually testing positive. In some ways, it is hardly a surprise that cruise ships can become hotbeds of infection: many are floating behemoths where those onboard interact frequently and at close quarters. Researchers also note that many of those onboard will have come from different countries, have travelled to different locations and have different degrees of immunity to diseases. What’s more, the ship moves. “Which means you have people potentially in contact with pathogens that they don’t encounter on the day to day,” says Dr Charlotte Hammer, an infectious diseases epidemiologist at the University of Cambridge. Throw in that a substantial proportion of passengers tend to be older adults, who may be more susceptible to certain diseases, and the scene appears set for potential disaster. David Heymann, a professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine, says: “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.” As Heymann points out, infections can be transmitted in different ways. One is through 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 on people directly or contam…