More than 400 passengers and crew have been sick with vomiting and diarrhoea as suspected norovirus hits two cruise ships sailing in the Caribbean.
Both luxury liners, the Queen Mary 2 and the Emerald Princess, reported the outbreak to the Centres for Disease Control, following guidelines that come into play when more than 2% of the passengers and crew are laid low.
The US public health agency said it was still conducting lab tests to determine the pathogen, but it said norovirus was suspected.
On Cunard's Queen Mary 2, which left New York on December 22 for a 10-day cruise, 194 passengers and 11 crew members of the more than 3,800 people were reported ill, the CDC said.
And on the Emerald Princess, owned by Princess Cruises, which returned to Fort Lauderdale on December 27, 189 passengers and 31 crew members of the more than 4,400 people on board fell sick, the CDC said.
The CDC said both liners had taken steps to stem the outbreak, including cleaning and disinfecting more often, as well as keeping passengers informed.
But Sue Hayes, from Arkansas, said she was on the Emerald Princess and her husband fell ill. She has been critical of how the crew members handled the crisis.
"It started just a couple of days into the cruise and has affected so many that the staff can't keep up with what they have to do for those who are sick," she said on Facebook.
"I have to phone to get the room cleaned because there aren't enough staff to even get clean towels and the room stewards are not allowed to come into the room.
"I have gone and got food for him because it may be a long time to get it delivered, like two hours after scheduled."
Some people who said they were on the Queen Mary 2 said on Cruise Critic that they were advised to avoid the buffet because of the sickness and that infected passengers were being kept in their rooms.
"I have never felt as sorry for the staff as I do now. They are working round the clock battling this situation," Andiamo said on the blog.
"It is serious, but in my opinion it is being handled very well.
"The festivities continue and those of us who have avoided this virus continue to enjoy the many offerings we come to expect and appreciate.
"For those passengers who have been exposed, they are confined to their cabins until declared safe to come out."
Sky News contacted both Cunard and Princess Cruises for comment but both companies said no one was available to comment.
Similar outbreaks hit two P&O luxury liners - the Azura and the Oriana - earlier this month.
The cruise ship infections come as norovirus is thought to be behind the deaths of four people in a hospital in Japan.
The patients, aged between 80 and 97, died of breathing problems and pneumonia last week after suffering vomiting and diarrhoea, said officials at Denentoshi Hospital in Yokohama.
Almost 100 other people have been infected at the hospital since Tuesday.
Norovirus has been sweeping the UK and has led to the closure of dozens of hospital wards.
The Health Protection Agency said there could have been more than a million cases in the UK this season.
The number of cases has risen earlier than expected this year, following an as-yet unexplained trend seen across Europe and other parts of the world.
Norovirus symptoms include sudden vomiting, diarrhoea, or both, a temperature, headache and stomach cramps. The bug usually goes away within a few days but can be contagious for a couple of days after vomiting has ended.