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Background  To control the presence of  Legionella  in an old hospital water system, an integrated strategy of water disinfection-filtration was implemented in the university hospital Umberto I in Rome.    Methods  Due to antiquated buildings, hospital water system design and hospital extension (38 buildings), shock hyperchlorination (sodium hypochlorite, 20–50 ppm of free chlorine at distal points for 1–2 h) followed by continuous hyperchlorination (0.5-1.0 mg/L at distal points) were adopted, and microbiological and chemical monitoring of the water supply was carried out in the university hospital (December 2006-December 2011).    Results  Overall, 1308 samples of cold <20°C (44.5%), mixed ≥20°C ≤ 45°C (37.7%) and hot >45°C (17.8%) water were collected, determining residual free chlorine (0.43 ± 0.44 mg/L), pH (7.43 ± 0.29) and trihalomethanes (8.97 ± 18.56 μg/L).  Legionella  was isolated in 102 (9.8%) out of 1.041 water samples without filters ( L. pneumophila  sg 1 17.6%,  L. pneumophila  sg 2–14 28.4%,  L.  non  pneumophila  53.9%), and in none of the 267 samples with filters.  Legionella  was recovered in 23 buildings out of 38 and 29 samples (28.4%) exceeded 10 3  cfu/L. When considering the disinfection treatment  Legionella  was isolated: before shock hyperchlorination (21.1%), 15 days after shock hyperchlorination (7.8%), 30 days after shock hyperchlorination (3.5%), during continuous hyperchlorination (5.5%) and without continuous hyperchlorination (27.3%). Continuous hyperchlorination following the shock treatment achieved >70% reduction of positive samples, whereas no continuous hyperchlorination after shock treatment was more frequently associated to  Legionella  isolation (OR 6.41; 95% CI 3.10–13.26; p <0.001). Independent risk factors for  Legionella  isolation were: residual free chlorine <0.5 mg/L (OR 13.0; 95% CI 1.37 – 123.2; p <0.03), water T° ≥20°C ≤ 45°C (OR 12.0; 95% CI 1.28 – 111.48; p <0.03) and no continuous hyperchlorination after shock treatment (OR 10.3; 95% CI 1.06 – 100.05; p <0.05).    Conclusions  Shock and continuous hyperchlorination achieved significant  Legionella  reduction, but effective chlorine levels (>0.5 < 1.0 mg/L) deteriorated water quality (organoleptic and chemical). However, shock and continuous hyperchlorination remains a valid-term option in old buildings with no water system rational design, managing problems due to hospital extension and absence of a proper hot water recirculation system.

Legionella control in the water system of antiquated hospital buildings by shock and continuous hyperchlorination: 5 years experience