The Norovirus, a nasty gastrointestinal virus, is preventing smooth sailing for some American travelers, with cases of the highly contagious virus skyrocketing to the highest numbers in the past decade.

There have been 13 outbreaks of Norovirus on cruise ships so far this year, according to reports from the U.S. Centers for Disease Control and Prevention (CDC). 

That marks the largest number of Norovirus incidents on these vessels in a single year since 2012—and the year is just halfway over.

The Holland America Line cruise ship

The Holland America Line cruise ship Zuiderdam, at anchor near the Forth Bridge, on June 29, 2023, in South Queens ferry, Scotland. (Ken Jack/Getty Images)

Cruise ship stateroom

A cruise ship statesroom. The CDC has reported thirteens outbreaks of Norovirus on cruise ships so far this year. (Mahmut Serdar Alakus/Anadolu Agency via Getty Images)

In 2022, there were just four outbreaks of the virus-despite peak travel times following the COVID-19 pandemic. There was a total of 235 guests and crew members that contracted the virus, according to the CDC.

According to the CDC, Norovirus is a highly infectious virus that causes inflammation in the stomach and intestines. Often labeled a "stomach bug," Norovirus is the most common cause of nausea, vomiting, diarrhea and stomach pain.

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The most recent outbreak occurred on Viking Cruises Viking Neptune ship. More than 100 passengers fell ill, according to the CDC, accounting for 13.1% of all vacationers on the ship.

Viking Cruises told the Wall Street Journal that it believes that the recent outbreak on its ship "originated from a shoreside restaurant in Iceland where a group of guests dined during their free time."

Royal Caribbean Celebrity Beyond cruise ship

The Martini Bar inside the Grand Plaza onboard the Royal Caribbean Celebrity Beyond cruise ship at Port Everglades in Fort Lauderdale, Florida (Eva Marie Uzcategui/Bloomberg via Getty Images)

Across the 13 outbreaks among cruises that docked in the U.S., nearly 1,700 passengers reported being ill during their voyages, along with more than 240 crew members. 

"Because cruise ships report illnesses to the CDC, there is more visibility and faster reporting to health authorities, which should not be confused to mean a higher incidence rate onboard," a spokesperson for the Cruise Lines International Association told WSJ.

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Other cruise lines impacted from Norovirus included: Celebrity Cruises, Holland America, Princess Cruises, Royal Caribbean International and P&O Cruises. 

The Anthem of the Seas cruise ship

The Anthem of the Seas cruise ship, owned by Royal Caribbean, is moored at PortMiami on February 07, 2023 in Miami, Florida.  (Joe Raedle/Getty Images)

The CDC reports outbreaks when 2% or more of passengers or crew report symptoms of gastrointestinal illness to the ship’s medical staff. Ships are required to report the illness within 15 days of arriving at a U.S. port. The ships also must have more than 100 passengers and sailings between three and 21 days long for an outbreak to be reported. 

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The CDC recommends washing hands, disinfecting surfaces with bleach, cooking food safely and washing laundry in hot water all help prevent the spread of the highly contagious virus.