There have been at least 16 outbreaks of gastrointestinal illness on cruise ships this year, the CDC says, the most in over a decade.

The Centers for Disease Control and Prevention has classified 2024 as the worst year for stomach illness outbreaks on cruise ships in over a decade as Norovirus cases surged in the U.S.

Norovirus, often coined the “cruise ship virus,” causes more than 90% of diarrheal disease outbreaks on cruise ships, according to the CDC. Still, norovirus outbreaks on cruise ships account for only a small percentage of all reported norovirus outbreaks.

Cruise ships saw the highest number of stomach bug illnesses since 2012 with 16 outbreaks that impacted 1,894 passengers.