Legionella pneumophila in Norwegian naval vessels

Little is known about the occurrence of Legionella pneumophila in water supply systems on board ships. Our aim was to study the occurrence of L. pneumophila in the water supply system on board Norwegian naval vessels as the basis for framing preventive strategies against Legionella infection.

Water samples were collected from technical installations and from the water distribution network on board 41 vessels and from ten water filling (bunkering) stations, the sampling taking place in two rounds separated by a one-year interval. The samples were subjected to analysis, including serotyping and genotyping, with a view to identifying the presence of L. pneumophila and of free-living amoebae.

L. pneumophila was found in 20 out of a total of 41 vessels in the first round of sampling, and live L. pneumophila serogroup 1 was isolated in seven of the 20 vessels. Free-living amoebae were found in the water supply system in most of the vessels, including all the vessels with L. pneumophila. The same genotype of L. pneumophila was identified in the water in bunkering stations and in the water on board the vessels.

L. pneumophila was not present in all the vessels, but all the vessels where the bacterium was found were also contaminated with free-living amoebae. We have demonstrated the probability of the fresh water from bunkering stations being the source of the contamination. In framing preventive strategies, importance should therefore be attached to identifying the source of contamination and the presence of free-living amoebae, as a premise for the establishment and growth of L. pneumophila in onboard water supply systems.