[Legionnaires' disease: 21 cases observed over 2.5 years in a Parisian respiratory intensive care unit].

The incidence of Legionnaire's disease is probably underestimated in France. Its clinical presentation is very suggestive, especially after the failure of a 48 hour therapeutic trial of beta-lactams, when a pneumococcal infection is initially suspected. This one sign is sufficient to orient the diagnostic survey and constitutes an indication for a therapeutic trial of macrolides for at least 72 hours. In fact, the delay in the diagnosis appears to be the determinant factor in the fatal outcome of the disease.