July 2 (UPI) — More than 120 people aboard a ship operated by Princess Cruises reported symptoms of norovirus, U.S. health officials said on Thursday.

The Ruby Princess was on a 20-day voyage along western North America when 102 passengers and 23 crew members on board reported gastrointestinal illness during the outbreak, the U.S. Centers for Disease Control and Prevention said in a statement.

The outbreak was first reported to the CDC’s Vessel Sanitation Program on June 28, according to the federal health agency.

Norovirus, a highly contagious virus, is the leading cause of vomiting, diarrhea and foodborne illness in the United States, according to the CDC. It causes acute gastroenteritis, an inflammation of the stomach or intestines, and is sometimes called the stomach flu.

The Ruby Princess had more than 3,000 passengers and 1,144 crew members aboard during the outbreak.

According to the CDC, Princess Cruises and the ship’s crew reported increased cleaning and disinfection procedures under the company’s outbreak prevention and response plan.

Crew members also collected stool specimens from cases for testing, isolated ill passengers and crew and consulted with the CDC’s Vessel Sanitation Program.

The Ruby Princess, with a capacity of 3,080 guests and 1,200 crew, had departed on June 12 from San Francisco and returned there following the 20-day voyage on Thursday.

UPI has contacted Princess Cruises for comment.

There have been seven outbreaks reported on cruise ships in the CDC’s jurisdiction so far this year, five of which were caused by norovirus.