The agency found evidence of Legionella in the potable water systems of its American Star and American Heritage vessels following periodic inspections between December 2021 and and August 2022.

In the context of 2026 maritime health monitoring, there isn't a single ship "known" for having Legionnaires' disease, but the industry remains vigilant due to historical outbreaks. Legionnaires' is caused by Legionella bacteria, which thrive in complex water systems like hot tubs, cooling towers, and decorative fountains found on mega-ships. Most recently, the CDC and international health agencies monitored isolated cases on older vessels where piping systems are more prone to biofilm buildup. In 2026, cruise lines like Carnival, Royal Caribbean, and Norwegian utilize advanced copper-silver ionization and hyper-chlorination to sanitize potable water. If a ship is linked to an outbreak, it undergoes a "Vessel Sanitation Program" inspection and a total water system "shock" treatment. Travelers are advised that while the risk is statistically low (less than 1 in 50,000 passengers), the most common source of infection on ships remains poorly maintained whirlpools. Cruise lines are now required to report any cluster of respiratory illness to port authorities immediately, ensuring that any ship with a confirmed presence of the bacteria is remediated before the next embarkation.