The Legionella bacterium is found in freshwater sources all over the world (1). The genus Legionella was not registered until 1979 – as a result of a major outbreak of Legionnaires’ disease among members of the American Legion (war veterans) in 1976, where Legionella pneumophila was found to be the cause (2, 3). The first bacterium isolate which was subsequently thought to be Legionella, was isolated in 1943 in guinea pigs and appeared similar to the obligate intracellular bacterium Rickettsia. In 1954 a similar bacterium was described, which was found to infect free-living amoebae. This isolate was classified in 1995 as Legionella (4).
Today, we know Legionella as a small waterborne bacterium which can be found freely present in water. It is highly fastidious as regards the substrate it requires for growth, and therefore survives and multiplies in other organisms, especially in free-living freshwater amoebae (5, 6). Legionella can cause respiratory disease in humans if a person inhales aerosolised water containing the bacterium. This exposure may occur daily if showering using water from contaminated water systems, although without it necessarily resulting in illness.
Infection with L. pneumophila is called Legionellosis. The infection usually presents as two distinct clinical entities: Legionnaires’ disease, a severe form of pneumonia with an approximately 30 % mortality rate; and Pontiac fever, an influenza-like illness of short duration (7). It has thus far not been demonstrated that these diseases can be transmitted from person to person (8).
To date, 53 different species of the Legionella bacterium have been identified (9), with some 20 of these being found in infections. The species L. pneumophila was found in more than 90 % of outbreaks and sporadic cases of Legionellosis, and more than 80 % of the L. pneumophila isolates belonged to serogroup 1 (10).
Legionella was registered in the 1980s and ’90s in outbreaks of disease with fatalities in Europe, but it was not until 2001 that the first outbreak occurred in Norway. It happened in Stavanger, where there were seven deaths (11), followed by an outbreak in Fredrikstad/Sarpsborg in 2005, with ten deaths (12, 13). As a consequence of the latter outbreak the statutory microbiological control in Norway has been made much stricter, including a regulatory requirement designed to prevent the spread of Legionella from whirlpool spas and shower systems (14). New guidance has also been issued for the control and prevention of Legionella infection (8).
The Legionella regulations and guidance impose a high degree of responsibility on owners of devices and systems capable of spreading aerosolised water. In order to comply with the requirements, owners need to have a knowledge of which factors in the relevant water supply system may contribute to the growth and spread of the Legionella bacterium.
Where the Nordic fleet is concerned, the requirement is for all freshwater supplies on board ship, for both food and hygiene purposes, to be of drinking water quality. The freshwater supply is obtained either by filling fresh water in port (bunkering) or by freshwater production onboard ship via desalination of sea water using reverse osmosis (RO) or evaporation (EVA) (15). For ships, freshwater production from sea water will be the optimal choice, since L. pneumophila is a freshwater bacterium not naturally found in sea water.
The Royal Norwegian Navy has a large fleet of vessels which are subject to the Legionella regulations. A project was started in 2010 aimed at establishing the necessary knowledge for Legionella control on board naval vessels. It included surveys and risk assessments to identify the occurrence of Legionella in the water supply systems of all naval vessels, for the purpose of establishing a basis upon which the Navy could take the necessary measures to prevent the occurrence, growth and infection by the bacterium.
We wish to thank Jadwiga Krusnell of the Swedish Institute of Communicable Disease Control, who introduced us to and assisted us in establishing amoeba diagnostics for the purpose of this study.