Prevalence of pneumonia due to Legionella pneumophila and Mycoplasma pneumoniae in a population admitted to a department of internal medicine.

We studied 177 patients with pneumonia admitted to an internal medicine department over a period of 3 years to determine the incidence of two emerging pathogens, Legionella pneumophila and Mycoplasma pneumoniae. Clinical, radiological and laboratory tests were performed and included blood cultures, serology, gram staining and sputum cultures. L. pneumophila was the agent involved in 9 patients (5.1%) and M. pneumoniae in 12 (6.8%). These prevalences were about in the middle of the range of previously published figures. Legionella pneumonia is a rare illness, which even in the absence of suggestive clinical signs must be considered because of its possibly serious course and to allow appropriate therapeutic decisions to be made.