LEGIONELLA - World Health Organization

The risk of legionellosis is increased for those on board ships where legionellae are present in
the water systems. Cruise vessels, in particular, have many similarities to hotels in the complexities
and operations of their water systems. The risks in ships may also be exacerbated in a number
of ways, outlined in Box 7.2.
Box . Factors exacerbat ng r sks on board sh ps
• When at sea, a ship is a closed environment, and might provide additional opportunities
for the transmission of airborne infection.
• Water storage and distribution systems on ships are complex, and may provide greater
opportunities for bacterial contamination as ship movement increases the risk of surge
and back-siphonage.
• The risk of sediments in tanks being resuspended and dispersed may be increased by
the ship’s movement and by adjustments to the water levels in tanks to maintain the
trim of the vessel.
• Loaded water may vary in quality and temperature.
• In some tropical regions, the risk of bacterial growth in the cold-water system is
increased because of higher ambient temperatures.
• Ships’ engine rooms are hot, and may affect water temperatures in pipes passing nearby.
• The movement of the ship could increase the potential for the formation of aerosols
(e.g. in air-conditioning ductwork) where there would not be an equivalent risk ashore.
• Proliferation could also result from long-term storage and stagnation of water in tanks
or pipes, and this risk could be increased when vessels are laid up for several months.
• Legionella can proliferate at temperatures sometimes experienced in stagnant warm
water in ships’ plumbing systems, especially in tropical regions, and in storage tanks on ships.
• Water can remain in a tank on a ship for a long time in comparison to on land, where
storage is usually for less than 24 hours.
Source: Edelstein & Cetron (1999)
Regional aspects — risk factors
Travel-associated infections tend to be diagnosed in the country of residence, because symptoms
are often recognized after the patient returns home. The incidence of legionellosis in tourists varies
with the country of residence or the outbound country, and the country of infection. The differences
may be attributable to differences in diagnostic rates or reporting, rather than to a difference in
susceptibility. Historically, the United Kingdom has reported more cases to EWGLINET than
other countries, but France, Italy, Germany and the Netherlands have increased their reporting
in recent years (EWGLI, 1999, 2001, 2004ab). This increase is probably due to a combination
of improved ascertainment (i.e. the determination through diagnostic methodology of whether
or not a person is infected with the disease) and improved surveillance. Cases from hotels have
also been reported from Japan (Suzuki et al., 2002); Sri Lanka (Wahala & Wickramasinghe,
2000); Beijing, China (Deng, 1993; Peng et al., 2000); Australia (Bell et al., 1996); Serbia and
Montenegro (Klismanicacute et al., 1990) and the Caribbean (Schlech et al., 1985).
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS