After years of decline, cases of norovirus infection rise on cruise ships

Whether from Miami, New York, Seattle or other cities, millions of Americans take cruise ships on vacation. But when it comes to the health of these travelers, that’s not always smooth sailing.

So far this year, there have been 13 outbreaks of norovirus on cruise ships, according to the US Centers for Disease Control and Prevention (CDC). This is the highest number of norovirus outbreaks on cruise ships since 2012.

The most recent outbreak of norovirus occurred on a trip from viking cruises of Iceland which docked in New York City on June 20. Around 13% of passengers and several crew members fell ill on board.

“We believe the gastrointestinal illness originated from a seaside restaurant in Iceland where a group of guests dined during their free time,” a Viking representative said.

“An extraordinarily contagious virus”

Norovirus is a highly infectious virus that causes inflammation of the stomach and intestines, a condition called acute gastroenteritis. Often labeled an “upset stomach,” norovirus is the most common cause of nausea, vomiting, diarrhea and stomach pain, according to the CDC.

A person can get norovirus by accidentally ingesting microscopic particles from feces or vomit – which can happen by coming into contact with someone who is infected, consuming contaminated food or water, or touching contaminated surfaces. Although symptoms usually only last a few days, a person can be infectious for as long as two weeks afterward.

“This is an extraordinarily contagious virus,” said Dr. William Schaffner, professor of infectious diseases at Vanderbilt University. “It only takes a few normal viral particles to start an infection in someone who is exposed. In other words, you don’t need a large dose.”

Although there is no medicine to treat the condition, most people recover fully without treatment. Hydration therapy to replace fluids lost through vomiting or diarrhea is standard practice to treat symptoms.

Still, to prevent the spread of norovirus, Schaffner recommends that cruise passengers take extra precautions and wash their hands thoroughly with soap and warm water. Antiseptic gels and hand sanitizers are not effective against the virus.

“As far as handwashing goes, we’ve all been doing it since we were kids,” said Jeffrey Fisher, associate professor of nutrition and dietetics at Central Michigan University. “But there are a lot of studies done that say we’re not doing it well enough or as often as we should. That’s why we want to revisit best handwashing practices.”

growing cases

The exact cause of the rise in cases on cruises this year is still unclear, but experts believe that rising demand for cruises and record passenger numbers could be behind it.

According to data from the CDC’s Vessel Sanitation Program, the number of norovirus outbreaks on cruise ships docked in US ports saw steady decline years after 2015. Overall rates of acute gastroenteritis on US cruise ships also declined from 2006 to 2019.

In response to the Covid-19 pandemic, the CDC instituted a health advisory with recommendations against traveling on cruise ships due to safety concerns. Cruises have been limited, CDC spokeswoman Kathleen Conley said, and outbreaks have been few as the number of passengers on board has declined.

In fact, the program did not record norovirus outbreaks in 2020 and 2021, likely due to limited cruises and updated sanitation protocols during the Covid-19 pandemic. In March 2022, however, the agency lifted that risk warning for cruise travel, and passengers are returning at record rates.

31.5 million passengers worldwide are expected to set sail this year, surpassing pre-pandemic levels and creating broadcast-ready high-density environments.

Norovirus outbreaks on cruise ships increase after years of decline
Halfway through the year, there are already more confirmed outbreaks in 2023 than there have been since 2012.

Confirmed annual outbreaks of norovirus on cruise ships

The CDC releases information about outbreaks on cruises with more than 100 guests traveling between three and 21 days, and when more than 3% of guests and crew report symptoms. These conditions have been met 13 times this year, up from twice in 2022.

Four norovirus outbreaks, involving a total of 449 guests and crew, have occurred aboard Royal Caribbean ships this year, the most for individual cruise lines, according to CDC data.

“The health and safety of our guests, crew and the communities we visit is our top priority,” said a Royal Caribbean International spokesperson. “To maintain the highest levels of health onboard our ships, we implement rigorous safety and cleanliness procedures, far exceeding public health guidelines.”

a perfect storm

Compared to the general population, norovirus outbreaks are quite uncommon on cruise ships. It infects 19 million to 21 million people in the U.S. each year, according to the CDC, compared with a few thousand cases aboard cruise ships.

Transmission often occurs in crowded environments where tiny particles can float in the air, and Schaffner says cruises can create the perfect environment for norovirus outbreaks. A large group living and eating nearby, he said, could serve as a breeding ground for the disease.

“It’s a closed population: a very large, compact population that is together for long periods of time, often in very tight quarters,” he said. “So there are many opportunities for people to meet […] making the transmission of this virus relatively easy.”

Norovirus symptoms can also come on suddenly, he said. A passenger may be walking to their cabin or attending an event and abruptly begin to vomit. This vomit is aerosolized and these floating microscopic particles can infect people nearby.

“You have this highly transmissible virus that is introduced into an environment, the cruise ship, ideally designed for the rapid spread of a communicable disease,” Schaffner said.

While symptoms like diarrhea and vomiting usually go away within a few days, they can also cause dehydration. For older passengers who can make up a disproportionate number of cruise customers, Schaffner warned, rapid fluid loss can create the risk of more serious illnesses. For people with diabetes, dehydration can undermine treatment strategies.

Fisher thinks that much of the problem stems from a “knowledge gap” about the virus among the public. “People are relaxing” as the Covid-19 pandemic seems to subside rather than remaining vigilant about the spread of disease.

“I think a lot of the public doesn’t even understand norovirus, let alone how to start protecting themselves,” he said. “They are not taking these precautions, these good protective behaviors that they learned during the pandemic.”

Schaffner also suspects that people who feel bad before boarding are now more inclined to sail. Looking forward to the holidays after a pandemic delay of 2½ years, many may be bringing the norovirus with them, he suggested.

“The first thing passengers can do is postpone their trip if they are not feeling well,” he recommended. “Try to limit other people’s direct exposure and take another cruise a month later.”

In addition to monitoring disease outbreaks onboard, the CDC’s Vessel Sanitation Program also requires periodic disease reports from cruise ships, conducts regular unannounced inspections, and conducts public health training for cruise ship employees.

As a precaution, the CDC advises passengers to wash their hands thoroughly, avoid contaminated food, and keep their hands away from their mouths. If a passenger becomes ill, Schaffner and the CDC recommend staying in the cabin and notifying the ship’s medical staff immediately.

“Let them take over and take care of you,” Schaffner said. “Don’t go out there and spread the virus.”