LEGIONELLA - World Health Organization

In hot tubs, the temperature of the water is within the optimal range for the growth of
legionellae (30–42 ºC).
Design, operation and maintenance — risk factors
Thermal water systems, including hot tubs, are at a high risk of being a source of potentially
pathogenic microorganisms, including Legionella, if they are not designed, installed, managed
and maintained with control of microbial growth in mind. This also applies to hot tubs on
display, whether or not they are used for bathing.
Hot tubs have a high bather-to-water ratio; they also have an extensive surface area within the
pipes used to provide both the air and water-driven turbulence. These pipes are often inaccessible
and difficult to clean and drain, and may also have areas of low flow or stagnation allowing
biofilms to form as illustrated in Figure 8.1. Pipework above the water line, such as pipework
supplying air to the jets, does not usually receive any disinfection from the pool water; its
interior is often humid and allows biofilms to form.
Many hot tubs provide no suitable access to all areas of the plumbing system, such as the
balance tank, for cleaning, disinfection and maintenance. High levels of legionellae have been
found in pools that had areas of pipework with stagnant water (deadlegs) as a result of
modifications made to the system.
Figure 8.1 Visible biofilm on internal pipework of a hot tub, two weeks after installation
Photograph courtesy of Susanne Surman-Lee
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS