LEGIONELLA - World Health Organization

Hot tubs that are not effectively designed, installed, maintained and managed have a high
risk of causing outbreaks of Legionnaires’ disease and Pontiac fever, even when not being used
for bathing. Further, hot tubs may be sold after having been on display for several months.
An important factor for manufacturers to consider is the risk of growth of Legionella after
construction and leak testing. Residual water left stagnant in the system will grow biofilm
microorganisms, which could infect the pool water after the system has been purchased and
refilled. Additional risk factors for hot tubs in commercial and domestic settings are detailed
in Box 8.3.
Box . Add t onal r sk factors for hot tubs n commerc al and domest c sett ngs
Commerc al sett ngs
• Heavy use can result in poor pH control and reduced concentrations of active biocide.
• Staff might not be aware of safety issues because of high staff turnover or short-term
employment, or because the hot tub is the only equipment that uses water (especially
in small clubs, for example).
• Operators might have insufficient information; for example, they might not know what
to do if parameters are tested and found to be outside the acceptable range.
Domest c sett ngs
• Owners often lack information or knowledge about the risks; they often also lack
training on treatment and maintenance regimes.
• Domestic spa pools are often located outdoors, where there are no convenient showers.
Dust and debris can enter the pool, and windy or breezy conditions can dissipate
biocide more rapidly.
• Consistent control can be difficult if the hot tub is used and dosed intermittently.
• A contaminated hosepipe might be used to fill the pool.
Because legionellae have been isolated from whirlpool baths, there is potential for infection
(Ishikawa et al., 2004; Susanne Surman-Lee, Health Protection Agency, United Kingdom,
personal communication, June 2005). Like hot tubs, whirlpool baths have an extensive array of
pipework beneath them, which provides a huge surface area for colonization.
Aerosols — risk factors
Bathers inhale aerosols at a short distance from the water surface, and the high humidity of
the environment increases the likelihood of survival of Legionella (Berendt, 1980; Hambleton
et al., 1983).
Various hydrotherapy treatments occur in some thermal spa resorts, including mouth irrigation,
vaginal douches and colonic irrigation. To date, there is no evidence of cases of Legionnaires’
disease directly linked to such procedures, but a risk assessment should take into account the
susceptibility of the users of such treatments.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS