Legionella: the Silent Passenger

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More than 20% of Legionnaires’ disease cases reported to the Centers for Disease Control are associated with travel, which includes travel on cruise ships. 

  • Contaminated hot tubs are the most commonly implicated shipboard sources; however, potable water systems have also been linked to transmission. From 1977-2012, there were 84 ship-associated cases of Legionnaires disease with 8 ships experiencing outbreaks of 2-50 cases; 6 cases were fatal.

Cruise ships are not the only maritime vessels at risk for Legionella colonization.

  • A recent study by Lagana et al surveyed 16 vessels (10 ferries, 6 cruise ships) docked in the port of Messina for the presence of Legionella in the potable water systems.
  • Legionella pneumophila was found on two (33%) of the 6 cruise ships. What is perhaps more interesting is the discovery of L. pneumophila on nine (90%) of 10 passenger ferries.
  • While all of the cruise ships reported having a routine water maintenance program, only one of the ferries had such a program in place. It was suggested that these vessels are more readily colonized with Legionella due to the age of the vessels and low use of the shower and washing facilities.
  • Some of the ferries contained crew and passenger cabins, creating a risk for longer-term exposure to contaminated water than would occur with transient passengers.
  • The authors of the study suggest that current European guidelines for passenger ships be modified to include specific requirements for ferries.

The risk of Legionella colonization can be decreased with proper treatment and maintenance programs.

  • The Centers for Disease Control and Prevention operate a Vessel Sanitation Program for vessels that have a foreign itinerary, call on a U.S. Port, and carry 13 or more passengers. Click here to see the full document.  This program stipulates that decorative fountains, humidifiers, misters, hot water systems, and showers be treated to prevent the growth of Legionella. The only way to be certain that the treatment program is working properly is to test for Legionella.
  • U.S. Micro-Solutions, Inc. accepts all types of water and swab samples for Legionella analysis. Our expertise, competitive pricing, and excellent customer service make us the first choice in environmental microbiology laboratories.