Hundreds of Royal Caribbean passengers were stricken with acute gastrointestinal ailments, including vomiting and diarrhea, on two cruise ships off the coasts of Mexico and California earlier this week. The debilitating illness was identified as norovirus, outbreaks of which aren’t uncommon on cruise ships, especially during the winter season.
Cruise line operators are required to report the total number of gastrointestinal cases, with online updates posted when they account for more than three percent of passengers and crew.
One of the two most recent outbreaks took place on the Legend of the Seas while on a two-week cruise that ended on Tuesday. It sickened 114 passengers, about seven percent of the total, as well as two crew members, according to the US Centers for Disease Control and Prevention (CDC).
The other outbreak struck the Infinity, part of the company’s Celebrity line, which reported 106 sick passengers, or about five percent of the total, on a cruise that ended Monday.
“During the sailing, we took a number of steps to prevent the transmission of the illness, including implementing enhanced cleaning procedures and protocols, and using special cleaning products and disinfectants that are proven to kill norovirus to clean throughout the ship,” a statement from Celebrity said.
According to the CDC website, a government health officer and an epidemiologist boarded the vessels in San Diego.
The two Royal Caribbean cruises marked the fourth and fifth outbreaks of norovirus at sea reported this year, the CDC said. That compares with eight in the same period in 2014 and four in the comparable period of 2013.
Norwegian Cruise Line Holdings Ltd’s Norwegian Pearl accounted for one of this year’s outbreaks, which involved 107 passengers on a cruise that ended April 6.
In an interview last year, Richard Fain, Royal Caribbean’s chairman and chief executive officer, said that such outbreaks are common on land. They get more attention on cruise lines because ship owners are required to report the data.
Worldwide, norovirus is the leading cause of acute gastroenteritis (inflammation of the stomach or intestines or both). About one in five cases of acute gastroenteritis, which leads to diarrhea and vomiting, is caused by norovirus.
Norovirus infections and outbreaks are usually more common in cooler, winter months. About half of all cases occur from December through February in countries above the equator, and June through August in countries below the equator.
In places closer to the equator, norovirus may be less seasonal. This may be because of temperature or the timing of the rainy season, among other factors.
The CDC’s Division of Viral Disease works with many global partners to identify the burden of acute gastroenteritis caused by norovirus and to prevent norovirus outbreaks throughout the world.