LEGIONELLA - World Health Organization

Given the complexity of distribution systems on ships, the chance of deadends and stagnation
is best reduced by proper design of storage tanks and pipes, both at the initial build and when
alterations are made, together with a flushing regime if water outlets are not being used regularly.
Preventing the risk of colonization during repair of the plumbing systems on ships deserves
special attention. Periodic maintenance and cleaning of the water storage tanks (i.e. draining,
physical cleaning and biocide treatment) should be carried out at least every six months.
Hot tubs and recreational pools — control measures
The risks from recreational pools and hot tubs on ships can be controlled in the same manner
as for pools on land, as described in Chapter 8 and in the World Health Organization Guidelines
for Safe Recreational Water Environments (WHO, 2006). The Centers for Disease Control in
the USA have issued guidelines for prevention of Legionnaires’ disease associated with hot
tubs on board cruise vessels (CDC, 1997b), and the Health Protection Agency (HPA) and
Health and Safety Executive (HSE) in the UK has also produced guidelines for management
of hot tubs, which are as applicable at sea as they are on land (HPA, 2006), and update earlier
guidelines published by the Public Health Laboratory Service (PHLS, 1994).
Air-conditioning — control measures
Humidifers or devices likely to amplify or disseminate the bacteria should be periodically
cleaned and replaced (Edelstein & Cetron, 1999). Special attention should be paid to the
proliferation of Legionella in humidifiers. Liquid should not be allowed to accumulate within
such units; they must drain freely and be easily accessible for cleaning.
7.4.2 Monitor control measures
Monitoring of systems in hotels and ships, including for facilities such as hot tubs and pools,
should largely follow the instructions set out in Chapters 4–6 and in Chapter 8.
Routine monitoring of the water system for Legionella has been used extensively in the hotel
sector, but its preventive efficacy is debatable; instead, WSPs are increasingly being recommended
and used in hotels.
If a source of Legionella transmission is identified, especially after an outbreak, a disinfecting
procedure (superheating or hyperchlorination) is recommended. Continued maintenance
and verification of controls should also be carried out.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS