LEGIONELLA - World Health Organization

Hosepipes may sometimes be used to fill hot tubs and other facilities. If the hose and/or
connectors have not been disinfected, the pool may be seeded with nuisance and harmful
microorganisms, such as Legionella and Pseudomonas aeruginosa, which will grow in damp
hosepipes left in warm environments.
Nutrients — risk factors
Nutrients for bacterial growth, originating from users of the facilities, are another factor to be
taken into account. The turbulence in hot tubs increases the risk of nutrients (e.g. dead skin
cells, cosmetics, body lotions and oils) being scoured from bathers. As the water is not drained
between users, the nutrients accumulate over the period of use, inactivating biocides and encouraging
microbial growth. Many users ignore advice to shower before using pools, increasing the
introduction of nutrients, faecal matter and urine.
Hot and cold-water systems — risk factors
A separate and additional risk of legionellosis arises from hot and cold-water systems including
showers in the vicinity of a swimming pool (Leoni & Legnani, 2001). Showers should be managed
as for hot and cold distribution systems in public buildings, and should be considered in the
Legionella risk assessment. Chapter 4 discusses risk assessments and control measures for piped
hot and cold-water systems.
Disinfection — risk factors
The bathing load, frequency of use and other factors that increase demand on the disinfectant
regime must be taken into account at the design stage. For example, hot tubs or natural spas in
health facilities that use seaweed therapies or mud treatments may have higher loads of nutrients.
In hot tubs in commercial premises, bathers often override the planned rest intervals (e.g. the water
and air jets automatically switching off for 5 minutes after every 15 minutes of use), which
would normally allow the hot tub to recover its effective disinfectant potential. The resulting
low disinfection residual increases the risk of colonization and growth of bacteria, including
legionellae. Bacteria colonizing and growing on surfaces (biofilms) are more resistant to biocides.
Temperature — risk factors
Legionella species can survive, but not grow significantly, in waters at temperatures below 25 ºC;
however, there is always a risk that legionellae will be present, albeit in small numbers, in the
water supplied to pools and their associated water systems (Hsu, Martin & Wentworth, 1984;
Ortiz-Roque & Hazen, 1987; Brooks et al., 2004).
Although the risk of Legionella growth is reduced in cold-water swimming pools, when water
is heated above 25 ºC, even in only part of the system, bacterial growth will occur in that region
and may then seed the rest of the system.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS