A gastrointestinal illness outbreak on a Royal Caribbean cruise ship sickened 180 passengers and three crew members with unpleasant symptoms like diarrhea and abdominal cramps, according to health officials.

Just under 9% of the 2,172 passengers onboard the Radiance of the Seas ship reported falling ill with the unknown sickness on its voyage to Alaska between Sept. 20 and Sept 27, according to the CDC.

In addition to the 180 vacationers, three of the 894 crew members also reported getting sick.

The infected passengers and crew experienced symptoms of diarrhea, abdominal cramps, headache, and muscle aches, according to the CDC.

Crew members alerted passengers of the outbreak and encouraged good hand hygiene via announcements on the ship and asked that anyone ill reported it to them. They also increased disinfection and cleaning measures to contain the outbreak.

"The health and safety of our guests, crew, and the communities we visit are our top priority," a Royal Caribbean spokesperson told USA TODAY in a statement. "To maintain an environment that supports the highest levels of health and safety onboard our ships, we implement rigorous cleaning procedures, many of which far exceed public health guidelines."

Royal Caribbean did not immediately respond to a request for comment.

Stool samples were collected from the sickened for testing, but the causative agent of the outbreak is not known, the health agency said.

The Royal Caribbean outbreak was the 10th outbreak to happen on cruise ships which include a stop at a US port this year, according to the CDC. The Norovirus was behind the majority of the outbreaks while E. coli was the cause of one.