Prevalence of Legionella spp. in swimming pool environment

A study was carried out to evaluate the prevalence of bacteria of the Legionella genus in the water from the pools and showers of 12 swimming pools in the city of Bologna (Italy). Sampling took place four times for every establishment, once for each season of the year. Legionella spp. were found in 2 of the 48 pool water samples (L. micdadei and L. bozenanii) and in 27 of the 48 samples taken from the hot water of the showers: 19 were positive for L. pneumophila (10-19,250 cfu/l) and 18 for other species (20-6000 cfu/l). The contamination was seen to be consistent throughout the year, since the same species of legionellae were isolated at different samplings and in concentrations that did not reveal any seasonal trend. The legionellae and the Gram negative bacteria were not found in shower water with a temperature above 43 degrees C. However, in the samples of shower water with a lower temperature a statistically significant inverse correlation was seen between legionellae and Pseudomonas aeruginosa (r = -0.51; p<0.01) as well as between legionellae and Gram negative bacteria (r = -0.70; p<0.01). The potential risk of contracting infections from Legionella spp. in the swimming pool environment does not seem to be linked to the pool water, but to that of the showers. The water temperature of showers should therefore be maintained at a level high enough to prevent the reproduction of these bacteria.