The Caribbean Princess arrived in Saint John Wednesday with 40 passengers and three crew members sick with a stomach flu. (CBC)

A cruise ship carrying dozens of passengers, who have been quarantined after contracting a stomach flu, arrived in Saint John Wednesday.

Roughly 40 passengers and three crew members aboard the Caribbean Princess have been plagued by an outbreak of the stomach flu.

The sick have been barred from leaving the cruise ship while it is in port in Saint John because the virus is easily spread.

John McCann, the Saint John port manager, said it only takes three percent of a ship's passengers getting sick to trigger a notice to Health Canada.

"They have some rudimentary lab facilities. So once they get an indication there could be a virus going around they take immediate steps to isolate it," McCann said.

The Caribbean Princess has about 3,100 passengers onboard.

Port officials say outbreaks like these happen on average once a year, usually later in the season when higher numbers of seniors are traveling.

The port officials plan to fully disinfect the terminal after the cruise ship leaves port Wednesday night.

Saint John businesses that serve large volumes of the cruise ship passengers were advised to take precautions.

Jenn Jewett, who serves coffee at Java Moose, said it was business as usual for her despite the warnings of the flu outbreak.

"We just have hand sanitizer that we're using just to keep the germs away," Jewett said.