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  • Writer's pictureP.K. Peterson

Germs Aboard Cruise Ships

“With infectious disease, without vaccines, there's no safety in numbers.”

Seth Berkley

Kentaro Iwata, Infection Control Specialist, criticizing ‘completely chaotic’ conditions on board a cruise ship quarantined in Japan

A little over a week has passed since the last Germ Gems post on the COVID-2019 epidemic, “Wuhan Pneumonia Update: Brace Yourself!” I’m sure you too are finding the daily news regarding this rapidly evolving epidemic very nerve-racking. By February 25, 80,348 cases of COVID-2019 had been confirmed, and 2,707 people had died (mortality rate ~3%), and SARS-CoV-2 infections had spread to 39 countries. On the 21st of February, 35 confirmed cases were reported in the U.S., including 21 “among repatriated individuals,” 18 of whom had been quarantined passengers on the cruise ship Diamond Princess.

To me, one of the most extraordinary aspects of this epidemic so far has been the quarantining of passengers aboard cruise ships. While everyone is likely aware of the pivotal role that air travel plays in transporting emerging pathogens around the world, little attention has been paid to germs that go along for the ride on cruise ships—the subject of this week’s post. (But before delving into this topic, let me point out that my focus is on a small number of germs, namely pathogens—microbes [germs] that cause disease. We’ll ignore the microbiome—germs that colonize our body surfaces, many of which are essential for health. Their numbers are truly astonishing. For example, if we just consider viruses, it is estimated that you harbor about 380 trillion of them [called your virome]. Thus a cruise ship carrying 1,000 passengers would transport about 380 quadrillion viruses. Of course, only an infinitesimally tiny fraction of these viruses are pathogens that can make someone sick, like SARS-CoV-2.)

A brief history of quarantining. Currently, there are no proven treatments for SARS-CoV-2 and experts say it could take a year or more to have a vaccine ready. Thus the hope is that strict quarantines in China and elsewhere will contain the virus' spread long enough for scientists to develop tools to fight it.

During my four decades as an infectious diseases physician, I can’t recall the quarantining of passengers on a ship to control the spread of an infection. This practice, however, has a long and interesting history. Quarantine, as we know it, began during the 14th century in an effort to protect coastal cities from plague epidemics. Ships arriving in Venice from infected ports were required to sit at anchor for 40 days before landing. This practice called quarantine was derived from the Italian words quaranta giorni, meaning forty days.

In the U.S., outbreaks of cholera from passenger ships arriving from Europe prompted a law in 1892 that provided the federal government more authority in imposing quarantine requirements. In 1944, the U.S. Public Health Service (PHS) was given the responsibility for preventing the introduction, transmission, and spread of communicable diseases from foreign countries into the U.S. A PHS cutter ship was used to transport quarantine inspectors to board ships flying the yellow quarantine flag. The flag was flown until quarantine and customs personnel inspected and cleared the ship to dock at the port.

In 1967, Quarantine was transferred to the Centers for Disease Control and Prevention (CDC). Currently, the CDC’s Division of Global Migration and Quarantine, headquartered in Atlanta, oversees some 19 Quarantine stations located in large cities throughout the U.S. Under its authority, the Division is empowered to detain, medically examine, or conditionally release individuals and wildlife suspected of carrying a communicable disease.

The list of quarantinable diseases includes cholera, diphtheria, active tuberculosis, plague, small pox, yellow fever, viral hemorrhagic fevers (such as Marburg, Ebola, and Congo-Crimean), and SARS. It seems likely that COVID-2019 will be added to the list. Quarantine Station personnel respond to reports of ill travelers aboard airplanes, ships, and at land border crossings to make an assessment of the public health risk and initiate an appropriate response.

Cruise ships carrying SARS-CoV-2. Two cruise ships were caught up in the COVID-2019 epidemic—the British ship Diamond Princess and the Holland America line MS Westerdam. The quarantining of passengers aboard the Diamond Princess by Japan captured the most attention. But many of the same lessons were learned from experiences on both ships—the main lesson: ships aren’t prepared to carry out proper quarantine procedures.

With justification both ships were referred to as “floating epidemiological disasters” or “floating Petri dishes.” For an excellent portrayal of the horrific situation on the Diamond Princess, see the February 22, 2020 New York Times article: ‘We’re in a Petri Dish’: How a Coronavirus Ravaged a Cruise Ship. As was pointed out by Michael Osterholm in a subsequent New York Times Commentary: “In light of the disease’s features, the quarantine of the passengers and crew members on the Diamond Princess cruise ship in Yokohama Bay in Japan looks like a cruel experiment: While confined, these people were forced to breathe recycled air for two weeks. The measure achieved little except to prove just how effective the virus is at spreading. Trying to stop influenza-like transmission is a bit like trying to stop the wind.”

In many ways a cruise ship provides a perfect environment for the sharing of viruses: overcrowding, inadequate ventilation, and a lot of socializing. After spending two weeks in quarantine, the 2,666 passengers aboard the Diamond Princess were evacuated from the port in Yokohama on February 18. By this time, 634 infections and two deaths caused by SARS-CoV-2 occurred, making it the largest outbreak outside of China.

The fate of the MS Westerdam and its 1,455 passengers differed from that of the Diamond Princess and raised additional concerns. After being shunned at port after port for fear it might carry SARS-CoV-2, when the ship arrived in Cambodia, the prime minister greeted its passengers with flowers.

Amid assurances that the ship was disease free, hundreds of elated passengers disembarked. Some went sightseeing, visiting beaches and restaurants and getting massages. Others traveled on to other destinations around the world.

One passenger, however, did not make it much farther than the thermal scanner at the Kuala Lumpur airport in Malaysia. The passenger, an American, later tested positive for SARS-CoV-2. On February 16, with passengers already headed for destinations on at least three continents, health officials were scrambling to determine how big a problem they now had—and how to stop it from getting bigger.

“We anticipated glitches, but I have to tell you I didn’t anticipate one of this magnitude,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center. With more than a thousand passengers from the Westerdam headed for home, Dr. Schaffner said, it may be harder than ever to keep the coronavirus outbreak contained to China. “This could be a turning point,” he said.

In dealing with the relieved Americans flying home from the Diamond Princess, 14 of whom were found to be SARS-CoV-2 positive just before boarding their flight, as well as those who vacated the MS Westerdam, the Quarantine Stations of the CDC’s Division of Global Migration and Quarantine had its hands full screening, quarantining, and monitoring them upon their arrival home.

Although I’m sure the repatriated passengers with COVID-2019 breathed a collective sigh of relief upon arrival back in the U.S., their troubles were far from over. In addition to battling their infection, they now found themselves stigmatized—a fate common for all people who have been quarantined. On top of that their dispersal to medical facilities for ongoing care was in some cases hampered. (One city in California sued the government to block transfer of COVID-2019 patients.)

Impact of COVID-2019 on the cruise ship industry. For now, the COVID-2019 epidemic remains centered in Asia, with recent spread from China to South Korea where on February 23 more than 600 cases were confirmed. Not surprisingly, the Princess Lines has cancelled voyages to Asia and the Norwegian Cruise Line has followed suit. Plus the U.S. State Department is warning travelers to reconsider Asian cruises.

In 2019, an estimated 30 million passengers travelled on cruise ships. So the economic impact of COVID-2019 clearly will hobble the cruise ship industry in Asia. Questions regarding the duration of travel bans and expansion to other areas of the world as well as to airlines are quite literally up in the air. Stay tuned.

Other pathogens you may encounter on cruise ships. A lot is still being learned about how SARS-CoV-2 is spread, but it appears that person-to-person transmission by airborne droplets is the main route of infection. Of course, other viruses, such as those that cause the common cold (rhinoviruses and other types of coronaviruses) and more importantly, influenza virus, also share this mode of transmission. So during the flu season, immunization against influenza before embarking on a cruise is highly recommended. And staying clear of coughing and sneezing travelers is a very good idea.

I’ve traveled on a cruise ship only once—a marvelous one week voyage through the Greek Isles two years ago. Aboard the cruise ship, it seemed almost impossible to walk more than a few hundred feet without running into a dispenser of the hand sanitizer Purell. Although washing my hands with soap and water was just as effective, this precautionary measure was aimed at preventing infection caused by norovirus, a virus that is spread by contaminated hands. The good news, however, is that I didn’t get sick and that the number of outbreaks of norovirus gastroenteritis aboard cruise ships has declined in recent years.

What everyone contemplating travel on a cruise ship needs to know. One of the challenges of trying to stay on top of the COVID-2019 epidemic is the overwhelming amount of information pouring in on this emerging infection. But the really good news is that the CDC provides continuously updated authoritative information on the epidemic including advice about travel on cruise ships. I highly recommend its website Before you sail or fly off to any foreign country, it’s always wise to pay it a visit.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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