The Ruby Princess docked in San Francisco on Thursday after a 20-day round-trip voyage to Canada and Alaska during which 125 people on board fell ill with norovirus, according to the US Centers for Disease Control and Prevention. The outbreak, which affected 102 of the 3,032 passengers and 23 of the 1,144 crew, was reported to the CDC on 27 June, though not all those infected were sick simultaneously. The ship’s operator, Princess Cruises, implemented enhanced sanitation protocols, isolated affected individuals, and conducted a thorough disinfection before the vessel departed on its next scheduled voyage later the same day.

Norovirus is a highly contagious pathogen that spreads rapidly in semi-enclosed environments such as cruise ships, often via contaminated food, surfaces, or direct person-to-person contact. Symptoms—predominantly sudden vomiting, diarrhoea, and stomach pain—typically resolve within three days, but the illness can be severe for young children, older adults, and those with underlying conditions. The CDC notes that handwashing with soap and water for at least 20 seconds is the most effective preventive measure, as alcohol-based hand sanitisers offer limited protection against the virus.

The incident is the seventh gastrointestinal illness outbreak on a cruise ship within the CDC’s jurisdiction so far in 2026, and the third this year involving a Princess Cruises vessel. Five of the seven outbreaks were caused by norovirus; the remaining two were attributed to E. coli. The cluster of shipboard infections this year has occurred alongside a separate hantavirus outbreak on the MV Hondius in the South Atlantic, which infected 13 people and resulted in three deaths. That outbreak was declared over in late May, with no new cases reported since.

Princess Cruises, headquartered in Santa Clarita, California, said the number of new cases on the Ruby Princess declined after the enhanced measures were introduced. The ship was cleaned and disinfected before embarking on its next trip from San Francisco’s Pier 27 on Thursday afternoon. Health officials continue to advise travellers to wash hands frequently and to seek medical attention if symptoms develop, while the CDC maintains its routine surveillance of gastrointestinal illnesses on cruise ships.