Background: This study aimed to demonstrate the importance of supervision practice in applying an operational plan to prevent legionellosis according to the I.S.S. 2015 guidelines.The protocol must be applied to hospital.There is the need for active surveillance corroborated by a rapid response when conditions of potential infections occur. So,monitoring contaminations with two different analytical methods(cultural and molecular biological) allowed prompt interventions finalized to restore normal conditions quickly.Furthermore,it was possible to determine the importance of water treatment upstream of the water distribution. Materials/methods: Pugliese-Ciaccio is a general hospital with 450 beds plus 58 beds in the oncology unit. The hospital adopted a protocol for preventing legionellosis, but it was not being fully implemented so far. Therefore, the followed protocol was applied, water was periodically sampled at a series of specific control points along the distribution system. An Ultra Violet (UV) lamp probed with electromagnetic spectrum UVC coupled with chemicals H2O2/Ag+ ions anti-corrosive product (phosphosilicates) was supplied to the water. Those parameters, in the emergency, were varied in concentration depending on the laboratory data. In addition, an additional UV lamp was installed at the return point of the hot water before entering the boilers. Results: During the period in which there was no complete monitoring of the procedures, the concentration of legionella had risen to very hazardous values beyond the consent upper limit.Thanks to our integrated actions, it was possible to bring them back into the safe environmental range shortly.About 1000 samples were taken during the study period at the various points at risk. Conclusions: A combined safety action amongst consultant, analysis laboratory and safeguarding made it possible to avoid potentially lethal infections for patients or staff. Furthermore, the quarterly frequency of sampling in the departments at risk has allowed for economic, fruitful, and effective management of the plants and security.