A norovirus outbreak has affected more than 100 individuals on a Princess Cruises ship.

Among the 3,001 passengers on the Ruby Princess cruise ship, 103 experienced illness during a voyage that concluded on Wednesday. Additionally, twelve crew members reported symptoms, primarily diarrhea and vomiting, as confirmed by the Centers for Disease Control and Prevention.

The Ruby Princess set sail from San Francisco on December 2, heading towards Hawaii and Mexico, as noted by CruiseMapper.

The cruise line has responded by enhancing sanitation measures onboard and isolating passengers and crew members who are ill, according to the CDC. Princess Cruises has yet to provide an official comment on the situation.

This year alone, the CDC has recorded 13 outbreaks of gastrointestinal illness on cruise ships that warranted public notification. Norovirus was identified as the cause in all but three of these cases.

While cruise-related illnesses are often highlighted, they represent only about 1% of all reported outbreaks.

“Cruise ships aren’t inherently different,” stated Dr. Sarah E. Hochman, who is a hospital epidemiologist and heads the infectious diseases section at NYU Langone Health’s Tisch Hospital. “Illnesses can occur in any crowded place, and they also happen in community settings on a smaller scale, like in homes among family members. These smaller instances may not garner public health attention like larger outbreaks do.”