Long read: Urgent action needed to prevent spread of COVID-19 on cruise ships

Passengers on virus-stricken cruise ship Zaandam, stranded off Panama in Central America. Credit: Luis ACOSTA/AFP via Getty Images

Cruise ships are being quarantined or barred from ports due to fears over the spread of the coronavirus disease 2019 (COVID-19), but evidence suggests that these vessels may be active breeding grounds for infection that unnecessarily endanger the lives of passengers and crew.

As COVID-19 rips through populations and countries close their borders to stem the infection, many cruise ships have found themselves caught in a limbo, either stranded at sea and prevented from docking or quarantined in port and unable to disembark.

For passengers and crew on board cruise ships, the nightmarish situation is compounded by the rapid spread of the virus as it jumps from person to person in close quarters. Many health experts believe the conditions of these vessels increase the rate of infection because people are encouraged to eat and socialise together and many of these trips are targeted at the elderly, who are particularly vulnerable once infected.

In the most high-profile case to date, some 700 of the 3,700 passengers and crew of Diamond Princess, operated by Princess Cruises, contracted COVID-19 after the ship was quarantined off the coast of Japan for 14 days in February 2020.

Seventy-eight cases were confirmed on board Grand Princess – another Princess Cruises vessel – when it was forced to anchor off the coast of California in the United States for about a week in early March. According to a report published by the US Centers for Disease Control and Prevention (CDC), 10 people on these two ships ultimately died.

The Cruise Lines International Association, which encompasses 38 cruise companies and more than 95% of global cruise capacity, made the difficult decision around the same time to temporarily suspend cruise lines departing from US ports until mid-April. However, many ships at sea are still struggling to complete their journeys.

Cruise vessels that are still seeking safe harbour include Holland America Line’s Zaandam, which was stranded off the coast of Panama after several Latin American countries refused to let it into port. With four passengers dead and dozens ill, it remains unclear where it will be allowed to dock.

Vessel numbers are mounting up at Sydney Harbour and surrounding coastline following Australia and New Zealand’s decision to bar many foreign ships.

Fears that offloading passengers will exacerbate COVID-19 spreading in ports and cities are understandable. However, there is evidence that forcing passengers and crew to remain on board, either at sea or in quarantine, can accelerate the rate of infection, resulting in much graver consequences for overall infections.

The cruise sector already has a questionable track record with viruses, specifically acute gastro-intestinal illnesses, such as norovirus. In 2019 alone, the CDC reported 10 virus outbreaks (9 norovirus, 1 unknown) on cruise ships.

In a stark message to US citizens, the CDC warned that people, especially those with underlying heath conditions, “should not travel by cruise ship” because there is an “increased risk of infection of COVID-19 in a cruise ship environment”.

A passenger is seen on a balcony of the Diamond Princess cruise ship during the quarantine of 3,600 people on board due to fears of COVID-19. Credit: CHARLY TRIBALLEAU/AFP via Getty Images

A study of infections on Diamond Princess, conducted by Umeå University in Sweden, concluded that the infection rate was about four times higher compared with land-side cases in the worst-infected areas of China.

The passengers who showed signs of illness were, as far as possible, separated from other passengers; still, several hundred became infected.

Joacim Rocklöv, professor of epidemiology at Umeå University and principal author of the study, said, “If the ship had been immediately evacuated upon arrival in Yokohama, and the passengers who tested positive for [COVID-19] and potential others in the risk zone had been taken care of, the scenario would have looked quite different. Our calculations show that only around 70 passengers would have been infected.”

He added, “The precautionary measure of putting the entire ship under quarantine was understandable, but due to the high risk of transmission on the ship, the decision is now questionable.”

The alternative option of quarantining people in facilities onshore may also be problematic and depended on the capabilities and facilities available. Many tourist destinations would struggle, even if the shipping company utilised its contracted medical assistance service.

Dr. Klaus Seidenstücker, a marine medical expert and former navy surgeon who trained ship doctors on cruise vessels, told SAS, “Countries are fighting to provide medical care for their own people, for example Italy and Spain are major cruise destinations terribly hit by [COVID-19], and may lack the logistical and medical capabilities to take thousands of passengers into their harbours.”

In addition, a lack of knowledge of the right way to contain the virus from spreading made it difficult for authorities to know the right action to take, so quarantine on board ships became one such mechanism.

“One option is the selective disembarkation of individual patients under suspicion of having the illness, removing them strictly either based on confirmed diagnosis and/or severity of symptoms,” said Dr. Seidenstücker.

Apart from infection being spread on vessels through people coming into close proximity or touching surfaces, evidence suggests that ships’ ventilation systems may fail to filter out germs or even encourage their movement around a ship.

A study published in 2016 by researchers at Purdue University examined the spread of flu on cruise ships. It found that one infected person on a 2,000-passenger cruise would typically result in more than 40 cases a week later, with transmission occurring through the ventilation system. That compared with just three new cases over the same time if transmission occurred on land.

Qingyan Chen, an expert on ventilation during virus outbreaks and co-author of the paper, asserted that air-conditioning systems on cruise ships were not designed to filter out particles as small as the COVID-19 virus, which allows the disease to circulate into other cabins.

In a statement he said, “It’s standard practice for the air-conditioning systems of cruise ships to mix outside air with inside air to save energy. The problem is that these systems can’t filter out particles smaller than 5,000 nanometres. If the coronavirus is about the same size as SARS, which is 120 nanometres in diameter, then the air-conditioning system would be carrying the virus to every cabin.”

He advised that cruise ships could minimise this problem by only using outside air and not recirculating it. Factors such as a lack of appropriate protective equipment or medical testing on board could also accelerate infection rates.

Marine consultant Captain Michael Lloyd told SAS, “Many crews do not have any appropriate PPE [personal protective equipment] for such an emergency, even though norovirus outbreaks have been going on for some time. There is no medical testing of crew immediately when they join a ship, instead it is left to the crewing agency in their home country.”

With COVID-19 potentially running rampant for many months to come and US-based cruise fleets due to remobilise in April, urgent action and intervention may be required to prevent many more people from becoming unnecessarily exposed to this invisible enemy.