Nearly 100 people were sickened by an outbreak of an unknown gastrointestinal illness this week on the Royal Caribbean cruise ship Radiance of the Seas, according to a report from the U.S. Centers for Disease Control and Prevention.

The CDC said on Feb. 5 that about 89 of the 2,164 passengers on the ship were affected by the outbreak, or about 4 percent of the passengers. Two out of 910 crew members reported symptoms, the agency said.

The primary symptoms, according to the CDC, are vomiting and diarrhea. The “causative agent” was listed as “unknown,” the agency also said.

The Radiance of the Seas trip started on Feb. 1 and is scheduled to end on Feb. 8, while the outbreak was first reported on Feb. 5.

Sick passengers and crew members were isolated from the rest of the individuals on the cruise ship, the CDC said. The ship also has stepped up “cleaning and disinfection procedures” and collected samples for testing to determine the nature of the outbreak, the agency said.

Officials with the CDC’s Vessel Sanitation Program are now “remotely monitoring the situation, including review of the ship’s outbreak response and sanitation procedures,” it added.

While the cause of the outbreak wasn’t disclosed, the CDC noted that norovirus is generally the cause of outbreaks on cruise ships and that “finding the agent that caused an outbreak ... can take time.”

“When an outbreak occurs, people whose symptoms met the case definition are asked to provide stool or vomitus samples. These samples are tested to determine the causative agent,” the CDC said.

Since the start of 2025, the CDC has reported six outbreaks on cruise ships, including the Radiance of the Seas trip. Three of the outbreaks were caused by norovirus, while one was caused by E. coli and other was “presumed” to have been caused by ciguatera fish poisoning, according to the agency.

Cruise ships are required to report cases where individuals report diarrhea or vomiting, along with other symptoms, to the CDC, the agency has said.

Norovirus Case Updates

The most recent numbers from the CDC show there were 97 outbreaks of norovirus reported during the week of Jan.9, although that was down from the 128 outbreaks reported a week earlier. Numbers from the past few years show a maximum of 65 outbreaks reported during that first week of December 2024.

A norovirus infection is characterized by sudden vomiting and diarrhea. Outbreaks are often seen on cruise ships, in congregate living situations such as nursing homes and jails, and in schools and places where people are close together.

In a normal year, according to the CDC, norovirus causes between 19 million and 21 million cases of vomiting and diarrhea, 109,000 hospitalizations, and 900 deaths across the United States. The virus also is associated with about 495,000 emergency department visits, mostly in younger children, the CDC says. Most outbreaks occur between November and April.

If there is a new strain of the virus, there can be upward of 50 percent more norovirus illness. the agency said. Norovirus outbreaks often occur in health care facilities, long-term care facilities, restaurants, child care centers, schools, and cruise ships.

The Epoch Times contacted Royal Caribbean for comment on Friday.

The Associated Press contributed to this report.