The line's Chief Executive Remi Bouysset said the current thinking was based on the latest medical and epidemiological information available.
"The indications strongly suggest the virus was introduced prior to embarkation and did not originate from the vessel itself," he said, adding: "Investigations remain ongoing regarding the exact location where the virus may have been contracted."
Bouysset described the outbreak, which resulted in three deaths from the rat-borne virus and "several others" falling serious ill, as "a human tragedy".
