PREVALENCE AND DIVERSITY OF LEGIONELLA PNEUMOPHILA IN THE DEFENSE SETTING

Legionella pneumophila (Lp) causes human infection, especially among susceptible individuals, following exposure to contaminated water aerosols generated by man-made water systems. Prevention of legionellosis builds on routine water inspection and corrective actions per national regulations. There are no data concerning the prevalence of Legionella spp. in water systems in the defense setting. This study thus aimed at estimating the prevalence of Legionella in samples obtained from a wide range of water systems in Israeli defense settings and explore the molecular epidemiology of these strains.

During 2015-2016, multiple samples were collected from water systems in 31 sites across Israel. Legionella was detected and enumerated per the ISO:11731 method. Sequence-based typing (SBT) was performed at the National Reference Laboratory for Legionella on a subset of Lp isolates and compared to the national database.

Of 191 water samples tested, 92 (46%) were positive for Legionella spp. and 71% of positive sampling points harboured Lp serogroup 1. In 45% of sampled sites, Legionella spp. counts exceeded the civilian regulatory threshold of 10³ CFU/L. SBT was performed on 88 strains and revealed 16 different sequence types (STs) including novel STs, which were subsequently deposited in the international database. The most abundant ST was ST1 (49%), which is also the most common ST found in clinical and environmental samples throughout the civilian sector in Israel.

This is the first study looking at the prevalence and diversity of Legionella in the defense setting in Israel. While the military population is generally considered healthy, the findings of this study suggest that the risk for acquiring legionellosis in the defense setting should be carefully assessed.