[Diagnosis of legionellosis].

The majority of legionellosis are caused by Legionella pneumophila, especially serogroup 1, the only diagnosed by Legionella urinary antigen test. The diagnosis of other serogroups and other Legionella species is based on culture and seroconversion. Sever cases are more frequently observed in immunocompromised patients and in nosocomial pneumonias. Each case must lead to look for the source of contamination, to detect other potential patients and permit environmental measures. Clinically and radiographically, the pneumonia is non specific except if suggestive gastro-enteric or neurologic symptoms are present. The diagnosis could be suspected in case of relative bradypnia or beta-lactamin resistance.