[How to reduce the risk of Legionnaires' disease?].

Legionella pneumophila is a microorganism present in water and able to develop pneumoniae through inhalation of contaminated aerosols. Legionnaires'disease is rare (1000 cases per year in France) concerning particularly people with risk factors, but potentially with severe prognosis (lethality 15-20%). The diagnosis was recently facilitated by the introduction of urinary antigen test. Hospital is the most frequent place where L. pneumophila were acquired; however the proportion of nosocomial cases is decreasing since 2001. The associated mortality is higher for hospital acquired cases than for community acquired cases. Several official guidelines were written about prevention of legionnaires' disease. Primary prevention is essentially based on control and maintaining of water-distribution system. Secondary prevention should be a prompt response to identification of a case in order to find the source of Legionella and to protect immunocompromised persons.