Legionella Control in the Water System of Antiquated Hospital Buildings with Hyperchlorination


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, report Orsi, et al. (2014). 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 one to two hours) 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).

Overall, 1,308 samples of cold <20[degree sign]C (44.5%), mixed >=20[degree sign]C <= 45[degree sign]C (37.7%) and hot >45[degree sign]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 mug/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 103 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[degree sign] >=20[degree sign]C <= 45[degree sign]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).

The researchers concluded that 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. Their research was published in BMC Infectious Diseases.

Reference: Giovanni Battista Orsi, Matteo Vitali, Lucia Marinelli, Veronica Ciorba, Daniela Tufi, Angela Del Cimmuto, Paolo Ursillo, Massimo Fabiani, Susi De Santis, Carmela Protano, Carolina Marzuillo and Maria De Giusti. Legionella control in the water system of antiquated hospital buildings by shock and continuous hyperchlorination: 5 years experience. BMC Infectious Diseases 2014, 14:394  doi:10.1186/1471-2334-14-394

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