Community-acquired pneumonia: is there difference in etiology between hospitalized and out-patients?

Since March 1991 a prospective 1-year study of patients with community-acquired, radiologically verified, pneumonia (CAP) was performed at the Divisione Pneumologica, Ospedali Riuniti Bergamo, and at the Centro Pneumo-Allergologico, Bergamo, Italy. The study included 119 out-patients and 60 in-patients, with a median age of 37.4 and 49.8 years respectively. There were not statistically significant differences between the patients included with respect to the various months. The most common underlying illnesses were: chronic obstructive pulmonary disease (20.7%), diabetes (7.3%) and malignancy (3.4%). We found a quite different etiology of CAP between out- and in-patients. By far the most common etiologic agent in out-patients was Mycoplasma pneumoniae (32.8%), while in in-patients was Legionella pneumophila (11.7%). 5 patients had a double infection. There were no distinctive clinical and radiological features found to be diagnostic for any etiologic agent. Hospital stay averaged 12.1 days. 35% of the patients included in the study were been treated by beta-lactam, often parenterally, nevertheless 88 pathogens of the 100 identified were resistant to this antimicrobial therapy. We believe that there should always be a macrolide, erythromycin or the latest ones such as azythromycin, in the treatment of CAP, owing to their efficiency, ease of use and lower cost.