Nearly 400 passengers and crew aboard 2 different cruise ships were throwing up last week — but not from seasickness. The U.S. Centers for Disease Control and Prevention reported Monday that at least 121 people traveling on Royal Caribbean’s Vision of the Seas and 276 people aboard Princess Cruises’ Ruby Princess fell ill with gastrointestinal symptoms last week. Illnesses were characterized by diarrhea and vomiting, likely caused by Norovirus, which infects the intestines and most commonly affects people in enclosed spaces such as cruise ships, daycares and nursing homes. The Vision of the Seas, which was returning from an 11-day voyage to the Caribbean, docked Friday in Port Everglades, Florida. A total of 118 out of the 1,991 passengers were sickened on that trip, as were 3 of the 765 crew members. Patients were treated for symptoms with over-the-counter medication available on the ship, according to a statement from Royal Caribbean. Royal Caribbean staff collected stool samples from 5 ill passengers and crew and submitted them to the CDC  for laboratory analysis. Staff also increased onboard sanitation measures during the outbreak. “During the sailing, we conduct enhanced cleaning onboard the ship, to help prevent the spread of the illness,” said Royal Caribbean in a statement. The boat left for its next the same day it arrived, after undergoing sanitization both onboard and at the cruise terminal, according to the company. Embarking passengers were notified of the illnesses that had occurred on the last trip. The Ruby Princess returned from a 7-day voyage to the Eastern Caribbean Sunday, docking in Fort Lauderdale, Florida. On that vessel, 266 of the 3,129 passengers fell ill, along with 10 of the 1,189 crew members. “At the first sign of higher-than-expected cases of illness aboard the Ruby Princess, the highest level of sanitation procedures were implemented, and these continued throughout the day before the next group of passengers boarded the ship (Sunday) afternoon,”  said Princess Cruises representative Karen Candy in an emailed statement to Food Safety News. “These pro-active procedures will continue throughout the subsequent cruise as well.”   CDC reports that staff “attempted collection of stool specimens from passenger and crew gastrointestinal illness cases” onboard the Ruby Princess while people were ill. The Ruby Princess, which also departed for another voyage the day she arrived, left a bit behind schedule Sunday after she was thoroughly disinfected and sanitized, noted Candy. Passengers boarding the ship for the next cruise were given a letter notifying them of the outbreak on the previous voyage, according to the CDC. Both vessels are scheduled to report to CDC’s Vessel Sanitation Program daily on their next voyages. Last year, CDC documented seven different Norovirus outbreaks on Princess Cruises’ boats. Two of these occurred on the Ruby Princess. Two Norovirus outbreaks were reported on Royal Caribbean cruises in 2012; one of them was on the Vision of the Seas.  Cruise ships have been working on improving sanitation methods to protect against Norovirus, which is transmitted via the fecal-oral route and spreads quickly among concentrated groups of people. Candy described Princess Cruises’ sanitation plan in the event of an outbreak:

– High-touch surfaces like railings, door handles and elevator buttons are thoroughly disinfected.

– Passengers are encouraged to use correct hand-washing procedures. To enhance this, hand sanitizing gels are placed throughout the ship.

– Ill passengers and affected crew should be isolated in cabins until non-contagious.

– Passengers are encouraged to use their own cabin’s bathroom facilities.

– Self-serve buffets are converted to full service.

– Staff make regular announcements and written communications to passengers outlining precautions to take while onboard.