Holland America Line’s Veendam was hit with a possible norovirus outbreak on its December 20-27 cruise, ending in San Diego on Sunday. Fifty-seven of 1,429 passengers or almost 4 percent of passengers were reported ill with vomiting and diarrhea as the primary symptoms, according to the U.S. Centers for Disease Control, which investigates illnesses on cruise ships.

Ten of 588 crew members, or 1.7 percent of the crew, also were ill during the cruise. While the CDC lists the causative agent as “unknown,” the reported symptoms mimic that of norovirus, which occurs on both land and sea in places where large numbers of people gather.

In response to the outbreak, the CDC said that Holland America Line and the crew undertook the following action:

Increased the onboard cleaning and disinfection procedures according to their outbreak prevention and response plan;

Collected stool specimens from passenger and crew gastrointestinal illness cases for testing;

Made twice daily reports of gastrointestinal illness cases to the Vessel Sanitation Program (VSP);

Consulted with the CDC on plans for their comprehensive sanitation procedures planned for the voyage disembarkation day in San Diego.

During that disembarkation, Holland America set up a planned staged disembarkation for active cases to limit the opportunity of illness transmission to other, non-infected guests and also sanitized the terminal, to protect those well passengers who were disembarking and others boarding the ship for the next cruise.