Two cruise ships operated by US-based operator Princess Cruises have been hit by outbreaks of norovirus that left nearly 500 people sick, reports CNN.

A total of 499 cases have been reported on the two ships, both based out of Fort Lauderdale in Florida. On Saturday, the ‘Crown Princess’ returned to port a Caribbean cruise with about 3,100 people were on board, of which 364 passengers and thirty crew members were sick. The following morning, 3,000 passengers and crew on board the ‘Ruby Princess’ disembarked, with 92 passengers and 13 crew members reported ill.

According to Princess Cruises spokesperson Julie Benson, the company, which is operated by Carnival Corporation, is working in co-operation with the US Centers for Disease Control and Prevention inspectors to establish the cause of the outbreak.

Symptoms of norovirus include diarrhea, vomiting and stomach pain. It is spread via person-to-person transmission or through contaminated food. Many outbreaks have been traced to food that was handled by one infected person.