They dismissed any link to a deadly hantavirus outbreak on another vessel that has put European health authorities on alert.
The Ambition was midway through a 14-night cruise from Belfast and Liverpool that was due to take in ports in northern Spain and along France's Atlantic coast.
It reached Bordeaux on Tuesday evening, according to the operator, Ambassador Cruise Line.
The US Centres for Disease Control and Prevention, which tracks outbreaks on voyages that call on US and foreign ports, recorded 23 gastrointestinal outbreaks on cruise ships last year.
Most were caused by norovirus, including a new strain.
Last week, a Caribbean Princess cruise ship reported a norovirus outbreak during a voyage with more than 3100 passengers aboard, according to the US health agency.
More than 140 passengers and 15 crew members fell ill during the trip, which ended Monday, the centre said.
The prefect of Nouvelle-Aquitaine region and Gironde department, Étienne Guyot, suspended disembarkation from the Ambition and restricted the vessel's interactions with the port of Bordeaux.
He acted on the recommendation of the regional health agency, the Agence Régionale de Santé Nouvelle-Aquitaine, the joint statement said.
Up to 50 passengers showed symptoms consistent with acute digestive infection after the ship's captain alerted French authorities on Tuesday evening, the statement said.
Those affected were treated by the ship's doctor and isolated in their cabins.
A medical team was dispatched to the vessel, and samples are being analysed at a Bordeaux hospital.
"There is no reason to establish a link between this outbreak aboard a cruise ship from Belfast and Liverpool and the hantavirus cases detected aboard the MV Hondius," the joint statement said.
The hantavirus outbreak aboard the Hondius last month prompted a multi-country response and the hospitalisation of passengers in Britain, France, Spain and the United States. Three passengers died and there have been nine confirmed cases, with another two suspected.
An update is expected later on Wednesday, once analysis results are available.
Ambassador Cruise Line said earlier Wednesday that a 92-year-old male passenger had died on Sunday, although he had not reported symptoms consistent with the illness, and that his cause of death was yet to be established by a coroner.
The company said 48 passengers and one crew member were displaying gastrointestinal symptoms as of late Wednesday morning.
Ambassador said its data showed cases had risen after passengers boarded in Liverpool on May 9.
All shore excursions at Bordeaux had been cancelled and affected passengers offered full refunds, the company said.
Ambassador Cruise Line, a British operator targeting passengers over 50, was founded in 2021.
10°C