LEGIONELLA - World Health Organization

Chapter 4 Potable water and
in-building distribution systems
Richard Bentham, Susanne Surman-Lee, John V Lee, Emmanuel Briand, Dick Van de Kooj
This chapter describes how a water safety plan (WSP) can be applied to assessing and managing
the risks associated with Legionella in potable water and in distribution systems in buildings.
It should be read in conjunction with Chapter 3, which discusses the different elements that
make up a WSP, and shows how a WSP fits within the framework for safe water quality
developed by the World Health Organization (WHO).
As explained in Chapter 3, a WSP has 10 steps that fit within the three main areas of system
assessment, monitoring and management and communications (see Figure 3.2). A WSP
must be comprehensive, and all 10 steps should be implemented in assessing and managing
the risks associated with Legionella. However, this chapter focuses on parts of the WSP where
information specific to potable water and in-building distribution systems is needed.
4.1 Background
The first published report of Legionella being transmitted through a potable water installation
involved renal transplant patients who acquired the infection in a hospital (Tobin et al., 1980;
see Chapter 6). Since then, Legionella has been observed in water systems in many different
types of buildings, including hotels, homes and factories, and in ships (Bartlett et al., 1983;
Habicht & Muller, 1988; Stout et al., 1992; Allen, Prempeh & Osman, 1999; Castellani Pastoris
et al., 1999). Legionella has been found throughout engineered water systems, from the mains
supply to consumers’ taps. Once present in a water system, legionellae can be isolated from a
range of sources, unless adequate controls are in place (Stout, Yu & Best, 1985; Colbourne
& Trew, 1986).
Legionella numbers in a plumbing system are influenced by many factors, and may vary considerably
in time and place, particularly in large, complex systems. Since legionellae can grow in association
with many different microorganisms (see Chapter 2, Section 2.3), it is important to control
other microorganisms to reduce the proliferation of legionellae.
Infection with Legionella requires both proliferation and exposure. Potable water systems
containing Legionella are a significant cause of sporadic cases of legionellosis acquired in the
community (Stout, Yu & Best, 1985; Yu, 1993; Venezia et al., 1994). Such systems are also the
main cause of nosocomial infection (through aspiration or direct infection of wounds —
Lowry &Tompkins, 1993), with cases reported in many European countries (e.g. see Box 4.1)
and in North America.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS