Comparison of procedures for controlling hot waterLegionella pneumophila contamination in health structuresP. Borella, I. Marchesi, P. Marchegiano, A. Bargellini, G. Ferranti,S. Cencetti

In a big hospital of northern Italy colonized by L. pneumophila, the effectiveness of various procedures in controlling contamination and preventing case onset was evaluated. Application of superheating showed the lest capability in reducing Legionella and is not suitable for large buildings as flushing with water >60°C at each outlet cannot reliably be maintained. In emerging situations, shock hyperchlorination is preferable as a more effective germ reduction method although requires higher manpower and pipes corrosion cannot be excluded. Point-of-care filters achieve the goal of 100% negative samples, and are adopted where transplant, oncological and other high risk patients are hospitalized. Also electric boilers installed on cold water line in high risk patient rooms guarantee absence of contamination, provided that temperature is maintained above 58°C. Continuoustreatment with chlorine dioxide is highly efficient in reducing germ concentration, but does not eradicate Legionella from the system, and at least 0.3 ppm at outlets are requested for the goal of L. pneumophila concentration below 100 cfu/L. More satisfactoryresults were obtained by injecting monochloramine, as control of contamination was evident just within the first month of application. Monochloramine level associated with germ below the detection limit approximate 3 ppm, but 2 ppm were sufficient for reducing legionellae below 100 cfu/L. Application of different procedures according to patient risk appear to be the best strategy and no cases of nosocomial Legionnaires’ disease were detected in the hospital during the observation period.