Gastrointestinal illness sickened more than 130 cruise ship passengers aboard a Royal Caribbean cruise earlier this month. The cause of the outbreak has not been determined.

Over 140 passengers and crew members aboard a Royal Caribbean International cruise ship were sickened by a gastrointestinal illness that led to vomiting and diarrhea, according to the Centers for Disease Control and Prevention.

The agency noted that cruise ships account for only about one percent of all reported gastrointestinal outbreaks, but the close quarters and shared facilities can make them particularly vulnerable to rapid spread.