Legionella contamination was studied in 34 nursing homes hot-water systems. A critical points analysis was conducted in each home in order to evaluate risk factors for occurrence of Legionella bacteria across four components of the water systems: cold water system feeding the hot-water production, hot-water production, hot-water distribution system and points-of-use. Risk factors were scaled according to criticity levels (1 to 4) and related to the prevalence and intensity of Legionella contamination. Hot-water of the nursing homes was contaminated by culturable Legionella (24.6%) and by Legionella detected using the in situ hybridization (FISH) technique (48.5%). Logistic regressions showed that criticity levels of hot-water system were predictive of hot-water contamination by culturable Legionella for two major components: "hot-water production" and "hot-water distribution system", and to a lesser extent for the "points-of-use" component. These results also hold true for the "points-of-use" criticity levels according to Legionella bacteria detected by FISH. In conclusion, because it shows a strong relationship between Legionella prevalence and critical points analysis of the water system, this study provides some tools for Legionella risk management.