LEGIONELLA - World Health Organization

United Kingdom regulations stipulate that a concentration of at least 0.2 mglitre free residual
chlorine should exist at all outlets, and that water storage tanks should be cleaned at least
annually with 50 mg/litre for at least four hours (Department of Transport, 1986), which is
often accomplished by supplementary chlorination in the storage tanks and in distribution.
Since it is often difficult to maintain cold water at less than 25 ºC on ships, supplementary
chlorination is required to maintain disinfectant residual throughout the system; a level of
free chlorine will contribute to the control of Legionella in such circumstances (WHO, 2004).
Water flow in the distribution system should also be maintained during periods of reduced
activity.
Disinfection — control measures
A study of 62 hotels in the Balearic Islands, Spain (Crespi et al., 1998) investigated the use of
continuous hyperchlorination at 1–2 parts per million (ppm) of free residual chlorine in the
cold water, and intermittent thermal treatment in the hot water. Samples positive for Legionella
dropped from a level of 32.4–31.3%, after the first year of application, to 20% after three years
and to 6% after five years. Another study evaluated the systematic purging of the hot and
cold-water pipes in two hotels with water chlorinated at 1–1.5 ppm of free residual chlorine
(Moreno et al., 1997). Negative cultures were not obtained in the two hotels until five and seven
months respectively after the treatment, highlighting the recalcitrant nature of legionellae
and the need for repeated and diligent disinfection.
Temperature — control measures
Some buildings may not be able to raise their hot-water temperature sufficiently to control
Legionella growth; therefore, an on-line treatment such as chlorine or copper/silver ionization
should be considered. Chapter 4 has more information on control measures relating to
temperature in distribution systems.
Design, operation and maintenance — control measures
The control of Legionella in water distribution systems in hotels is difficult, and requires the
continuous and effective maintenance of preventive measures.
Hotel personnel responsible for the maintenance of hotel water systems must be educated
and qualified to perform these duties. The importance of training and education has been
recognized in a large number of published preventive guides. Data from the application of
training programmes are very encouraging, and suggest that education may be important in
preventing legionellosis in the tourist sector (Crespi & Ferra, 2002).
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS