LEGIONELLA - World Health Organization

Where the design of swimming pools or other recreational water-based facilities includes a
water feature created spray (e.g. a fountain), the potential for transmission of legionellae from
aerosols should be considered.
System assessments of hot tubs have revealed an array of factors contributing to unhygienic
conditions and, potentially, predisposition to legionellae proliferation (see Box 8.2).
Box . Examples of problems found w th balance tanks n hot tubs n commerc al
sett ngs after a system assessment
Problems identified with balance tanks during investigations of poor microbial quality in
hot tubs include:
• tanks found bricked up behind wall
• a tank with a shower built on top of it
• several tanks buried beneath the hot tub, so that access for cleaning is not possible
• tanks constructed of materials that are difficult to clean, such as rough concrete
• some tanks underground, within confined spaces, creating access problems for cleaning
• one tank found to contain large amounts of builders’ rubble.
8.3.3 Assess hazards and prioritize risks
This section discusses generic risk factors, in line with the preceding chapters. Where appropriate,
and for ease of reference, it also looks specifically at recreational facilities such as hot tubs,
although this creates some repetition of information.
Source water quality — risk factors
In pools, the quality of source water is an important factor in preventing microbial growth within
the system. Where the source contains high numbers of background heterotrophic microorganisms,
or is high in organic content, there is potential for growth of Legionella in parts of the water
system that may be subject to a rise in temperature (e.g. in storage systems or near underwater
lighting or pumps).
Mineral water taken from hot springs is widely used in many spa treatment centres, where it
is claimed to be beneficial for relaxation and for its therapeutic effects. The thermal water, which
is high in mineral content, is usually drawn from underground boreholes, collected and then
distributed. Samples from these boreholes may contain small numbers of legionellae, but
high levels have been detected where such water is stored before distribution (Martinelli et al.,
2001). As many as seven different Legionella species or serogroups have been found in one thermal
water distribution system at a spa in the Czech Republic. The high mineral content of these
hot spring waters leads to deposition of scale on surfaces in the distribution network, increasing
the surface area for bacterial colonization.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS