Figures from France's military leadership show more than half the sailors aboard the country's flagship aircraft carrier contracted the new virus as the ship traveled through the Mediterranean Sea, the North Sea and the Atlantic Ocean.
A navy official says 1,046 of the 1,760 people aboard the Charles de Gaulle tested positive for the virus.
Navy Chief of Staff Adm. Christophe Prazuck attributed the quick spread to the great population density aboard the ship. Speaking Saturday evening to Europe-1 radio, Prazuck said virus protection measures weren't followed properly, which did not allow us to detect the beginning of the epidemic, and therefore to contain it.
The ship is undergoing a lengthy disinfection process since returning to its home base in Toulon last week.
One person who served aboard is in intensive care and more than 20 others are hospitalized. Among those infected are two U.S. sailors serving as part of an exchange program.
Investigations are underway into what happened, and French military leaders have been questioned in parliament.
A similar outbreak on the USS Theodore Roosevelt led to the firing of its captain and the resignation of the acting U.S. Navy secretary.