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Background: Legionnaires’ disease (LD) occurs predominantly in adults and elderly people. Its incidence in Europe has been increasing in recent years. It is rare in younger age groups and prone to be reported as healthcare-associated infection with a higher risk of fatal outcome. Hospital-acquired LD is mostly associated with a colonized hospital water system. We describe 5 LD cases in a children’s hospital in Slovakia, subsequent environmental investigation, control measures, and 5-year monitoring of Legionella colonization in hospital’s water system. Methods: In 2014–2019, we tested clinical specimens from 75 hospitalized patients. Respiratory samples were cultured for Legionella, patient’s urine was tested for Legionella urinary antigens, and the microagglutination test was used for serologic testing. Samples of water were collected in 2015–2019 and processed according ISO11731. Results: We identified 5 Legionella infections in 2014–2015. Median age of patients was 15 years. All were high-risk patients hospitalized for their underlying diseases. All patients required admission to intensive care unit, and artificial ventilation due to general deterioration and respiratory failure. Legionella pneumophila was isolated from 72% of water samples. Chlorine dioxide dosing into water system above 0.3 ppm caused significant decrease of Legionella concentration in water samples. Samples taken from outlets with antimicrobial filter installed were legionellae-negative. Conclusions: Control measures led to decreased risk of infection, but not to eradication of Legionellae. It is necessary to extend the diagnostics for Legionella infection in hospitalized children with pneumonia, especially in hospitals with colonized water system.

Background: Community-acquired cases of Legionella infection or even outbreaks can be attributed to inhalation of aerosols from devices such as hot water system, cooling towers, hot tubs, industrial equipment and indoor fountains. Legionellae survive in water in temperatures between 20 °C and 50 °C and tend to colonize particularly water systems rich of sludge, rust, biofilms and amoebae where they can multiply. Cooling towers (CT) in industry are used as heat-transfer devices in which warm water is cooled by evaporation in atmospheric air. Aerosols can transmit Legionellae to susceptible hosts, who can contract either Legionnaires´ disease (elderly with many risk factors) or Pontiac fever (young or middle-aged people relatively healthy without any risk factors). Aim: Aim of the study was risk assessment of legionellosis for workers in contact with contaminated water aerosol from industrial cooling towers. Methods: Water samples from industrial cooling towers and air samples were processed by standard manner (EN ISO 11731) and plated on special buffered charcoal yeast extract agar with 0.1% ketoglutarate and L-cysteine (BCYα medium) containing glycine, vancomycin, polymyxin B, cycloheximide (GVPC medium) for Legionella isolation. Exposure of workers to water aerosols was evaluated by interview, questionnaire, serological testing (agglutination test), cultivation of sputum on BMPA (BCYα medium with cefamandole, polymyxin B, anisomycin), detection of Legionella antigen in urine by ELISA and DNA Legionella in sera by PCR. Results: Sampling water from 6 cooling towers revealed isolates of Legionella pneumophila (L.p.) serogroups 1, 5, 10 from four of them (1,6 × 10 2-1,49 × 10 4 /200 ml). Investigation of air around three CT showed contamination by L. p. serogroup 12 in one of them. Antibodies only against this L. p. serogroup 12 were detected in single sera (1:128-1:256) in 13 workers, i.e. in two external workers working directly inside CT (diving) and 11 internal workers, who attended instruction meeting lasting several hours close to this tower. The workers contracted non-pneumonic infection-Pontiac fever with mild clinical symptoms. Conclusion: Exposure to water aerosols produced by the industrial cooling tower led to the cluster of non-pneumonic professional Legionella infection in workers. Results of the study were used for recommendation of repressive (disinfection, operating regimen of towers) and preventive (respiratory protective equipment, monitoring of Legionella colonization, etc.) measures.