Surveillance of Legionella pneumophila: Detection in Public Swimming Pool Environment

Abstract

The bacterium Legionella pneumophila is a ubiquitous microorganism naturally present in water environments. The actual presence of this opportunistic premise plumbing pathogen in recreational swimming pools and hot tubs in the northwestern part of Croatia has not been investigated. This study aimed to analyze the presence of the opportunistic pathogen L. pneumophila in public swimming pool water in Primorje-Gorski Kotar County (N = 4587) over a four-year period (2018-2021). Additionally, the second aim was to investigate the connection between the presence of L. pneumophila and pool water physicochemical parameters using mathematical predictive models. The presence of L. pneumophila was detected in six pool samples. Five positive samples were found in the water of indoor hot tubs filled with fresh water, and one positive sample in an outdoor recreational saltwater pool. A predictive mathematical model showed the simultaneous influence of chemical parameters dominated by the temperature in saltwater and freshwater pools, as well as the significant influence of free residual chlorine and trihalomethanes. Our results pointed out that keeping all physicochemical parameters in perfect harmony is necessary to reach the best disinfection procedure and to avoid the optimum conditions for L. pneumophila occurrence.

Keywords: Legionella spp.; physicochemical parameters; prevention; recreational water; swimming pool water.

Figure 1

Water’s physicochemical parameters: (a) temperature (°C), pH and free residual chlorine (FRC; mg/L), and (b) trihalomethanes (THM; μg/L) and amount of Legionella pneumophila (CFU/L) in outdoor and indoor swimming pools. Results are shown as median, minimum, and maximum values, with outliers and extreme values (N_{pool data} = 4587; N_{outdoor data} = 2233; N_{indoor data} = 2354).

Figure 2

Water physicochemical parameters: (a) temperature (°C), pH, and free residual chlorine (FRC; mg/L), and (b) trihalomethanes (THM; μg/L) and amount of Legionella pneumophila (CFU/L) in children’s, recreational, hot tubs, and sports/Olympic swimming pools. Results are shown as median, minimum, and maximum values with outliers and extreme values (N_{pool data} = 4587; N_{children’s data} = 495; N_{recreational data} = 2833; N_{hot tubs data} = 966; N_{sport/Olympic data} = 293).

Figure 3

Water physicochemical parameters: (a) temperature (°C), pH, and free residual chlorine (FRC; mg/L), and (b) trihalomethanes (THM; μg/L) and amount of Legionella pneumophila (CFU/L) in swimming pools with fresh and salt water. Results are shown as median, minimum, and maximum values with outliers and extreme values (N_{pool data} = 4587; N_{saltwater data} = 1478; N_{freshwater data} = 3109).

Figure 4

Distribution of analyzed swimming pool water’s physicochemical parameters (temperature (°C), pH, trihalomethanes (THM; μg/L), free residual chlorine (FRC; mg/L)), and bacteria: Legionella pneumophila (CFU/L), depending on whether it was an indoor or outdoor swimming pool and the type of swimming pool (children’s, recreational, hot tub, or sports/Olympic), as determined by principal component analysis (PCA) with main components PC 1 and PC 2. Projections of (a) the variables (swimming water pools’ physicochemical parameters and bacteria) and (b) cases (type of swimming pools and outdoor or indoor conditions) on the factor plane. (N_{pool data} = 4587; N_{outdoor data} = 2233; N_{indoor data} = 2354).

Figure 5

Distribution of analyzed swimming pool water’s chemical parameters (temperature (°C), pH, trihalomethanes (THM; μg/L), free residual chlorine (FRC; mg/L)), and bacteria: Legionella pneumophila (CFU/L) depending on water in the swimming pool (saltwater or freshwater) and type of swimming pool (children’s, recreational, hot tub, or sports/Olympic), represented by principal component analysis (PCA) with main components PC 1 and PC 2. Projections of (a) the variables (swimming pool water’s chemical parameters and bacteria) and (b) cases (type of swimming pools and water in the swimming pools) on the factor plane. (N_{pool data} = 4587; N_{saltwater data} = 1478; N_{freshwater data} = 3109).