Hospital-acquired Legionella infections: an update on the procedures for controlling environmental contamination

The waterborne healthcare-associated infections are mainly sustained by Legionella and Pseudomonas spp. Various water factors and plumbing characteristics, and the interaction with other water microorganisms are considered to be predictive of Legionella contamination. It is therefore mandatory to organize plans of surveillance, prevention and control in order to avoid disease appearance in immunosuppressed patients, with higher risk of death. Guidelines for the prevention of Legionnaires' disease have been published, benefiting those who face this problem, but definitive standardized solutions do not exist yet. Here we describe fifteen years of activity, during which our study group gathered interesting data on the control of Legionella contamination. Water disinfection is not generally sufficient to control the risk of infection, but a complex water safety plan should be developed, including system maintenance, training of staff and implementation of a clinical surveillance system aimed at early detection of cases. Concerning the control measures, we evaluated the effectiveness of different treatments suggested to reduce Legionella spp contamination, comparing our results with the current literature data. The performance ranking was highest for the filter, followed by boilers at high temperature, monochloramine and, at a lower level, chlorine dioxide; the effectiveness of hyperchlorination was limited, and thermal shock was even more ineffective.