Legionellosis risk in swimming pool and SPA

Spas used for either therapeutic or recreational aims are considered at risk for legionellosis occurrence. Thermal water is normally used at temperature between 30 and 40°C, ideal for Legionella growth, with a potential risk for users. Inhalation of colonized aerosol has been associated with sporadic cases or clusters of both Legionnaires’ disease and Pontiac fever, particularly involving immune depressed subjects. Italian and European guidelines have been issued to prevent and control this risk. At the spring, thermal water can contain small concentrations of legionellae, but within the distribution lines the amplification of these bacteria is promoted by stagnancy and incrustation, a frequent phenomenon also associated with the high mineral content of these waters. In addition, the detachment of dead cells, body lotions/creams residuals and skin debris in swimming pools favorites the bacteria multiplication. The devices/treatments more involved in transmission risk are inhalation therapies, frequently utilized by persons with chronic disease, showers and whirlpools, largely used also in the wellness centers. We revised the studies on Legionella spp presence in hot springs and related structures. The majority of published reports documented the germ contamination both at the source and along the distribution lines up to the point of use with increasing concentrations. Particular water characteristics such as high levels of sulfur and/or carbonate seem to be unfavorable to legionellae colonization but further studies are needed to deep this aspect. Contamination risk is less relevant for swimming pools due to high chlorine content, unless an insufficient disinfection plan is applied. From eighty years, about 50 studies have been published documenting cases of Legionnaires’ disease associated with spas. The majority of them occurred in Japan, where also a large outbreak is described with more than 300 persons involved. In almost all cases, L. pneumophila was the responsible germ and during the environmental inquire Legionella spp was found in many points of the spas: in spring water, in the distribution system, in the tank, in devices for nasal irrigation and aerosol therapy as well as in the whirlpool bath and swimming pool. To study the infection risk, the antibodies against Legionella have been evaluated in workers and patients attending the spa; the antibodies presence was found in a decreasing proportion from therapists to administration personnel. In conclusion, we underline the need for an accurate surveillance and control of Legionella spp and other waterborne germs in spas and other structures where inhalation of aerosolized water is expected.