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.

A gastrointestinal outbreak aboard a Royal Caribbean cruise sickened more than 140 people earlier this month, according to a report from the Center for Disease Control and Prevention’s Vessel Sanitation Program.

The US CDC has launched an investigation after passengers on the Royal Caribbean cruise started showing signs of acute gastroenteritis (AGE), which is usually caused by norovirus