A total of 158 people contracted norovirus gastroenteritis on a Diamond Princess cruise ship that docked in Sydney, Australia on Sunday, AOL Travel reported

According to MSN, all of the infected travelers were treated by the ship's doctor. 

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"I just got sick Monday night, vomiting and gastric (issues)," MSN reported a passenger said. "I was in bed Tuesday."

Approximately 4,000 people were aboard the ship, operated by Princess Cruises, as it returned Sydney from a 12-day cruise to New Zealand.

 

What may have caused the virus to spread

One passenger told ABC she thought an ill passenger who failed to report sickness was the cause of the widespread virus. 

"Somebody had come on five days earlier and hadn't reported it, so that's obviously what started it off," she said. "When anyone got sick you were supposed to report it to (the ship's crew) immediately, then you were quarantined."

Many passengers said the cruise line handled the situation well.

"We were very well informed; they let us know when there was an outbreak and they informed all the passengers regularly about the measures they were taking to stop the spread," she said. "In the restaurants they stopped self-serving, and we were served by the attendants, so we weren't allowed to touch anything. They let us know they had it under control."

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Travel site Cruise Critic says the illness is "not a 'cruise ship' virus." It can also be spread in nursing homes, restaurants, hotels and dormitories.

"Norovirus spreads swiftly wherever there are many people in a small area," the organization wrote.

Symptoms of norovirus include nausea, vomiting, diarrhea and abdominal cramps.

"Norovirus is associated with cruise travel simply because health officials are required to track illnesses on ships, and (they) are not (required to do so) at hotels and resorts; therefore, outbreaks are found and reported more quickly at sea than on land," Cruise Critic reported. 

The Centers for Disease Control and Prevention estimates that there are more than 20 million cases of norovirus annually.