July 18 (UPI) — The U.S. Centers for Disease Control and Prevention has announced that an unknown illness sickened more than 100 people aboard a Royal Caribbean cruise ship earlier this month.

According to a press release from the CDC’s Vessel Sanitation Program, a “gastrointestinal illness outbreak” occurred on the Navigator of the Seas that traveled round-trip to Mexico from Los Angeles between July 4 and11.

Out of the 3,914 passengers, 134 reported being ill, as did seven crew members. The victims experienced symptoms that included abdominal cramps, diarrhea and vomiting, but the CDC reports that the “causative agent” has not been determined.

The ship’s crew took preemptive measures for passengers by isolating sick and then collected stool specimens from them for testing. Cleaning and disinfection procedures were also implemented and the CDC notified.

Statistics from the Vessel Sanitation Program show 18 bouts of gastrointestinal illness aboard cruise ships under the program’s authority in, which ties for the total amount in all of 2024.

There were only 14 in all of 2023, but a CDC spokesperson told USA Today in April that although “the number of recent cruise ship outbreaks has been higher than in years prior to the pandemic, we do not yet know if this represents a new trend.”