[Legionella and legionellosis: of water, bacteria and men]

Legionella species are natural dwellers of stagnant waters. Inhalation of contaminated aerosols may result in pneumonia, with a noteworthy mortality rate (20%). However, such infections are infrequent, when compared to the rate of human exposition to Legionella. Legionellosis apparently occurs in patients in which respiratory tract macrophages allow bacterial replication, especially that of Legionella pneumophila serogroup 1. Following a silent incubation period, large amounts of bacteria are released, resulting in a strong inflammatory response responsible for the severity of symptoms. The outcome depends on quick establishment of antibiotic therapy and early diagnosis is therefore necessary. Nowadays, the risk of acquiring legionellosis raises passionate discussions, in which the presence of Legionella in man-made water systems is often assimilated with the disease itself. Significant efforts are being made to detect and monitor the amount of Legionella in potentially contaminant environments. However, the prevention of legionellosis also requires that research efforts for a better understanding of the virulence mechanisms of infective strains are carried out.