Background: A one year prospective study was carried out to assess the etiology of community-acquired pneumonia (CAP), and also to know the incidence, characteristics and evolution of infection by Chlamydia pneumoniae; and the effectiveness of DNA probes in CAP due to Mycoplasma pneumoniae and Legionella.
Methods: One hundred and ten patients with a diagnosis of CAP in the emergency department were studied. Serologic studies were performed, and also tests commonly used for the diagnosis of respiratory tract pathogens in respiratory samples, including serology and culture of Chlamydia pneumoniae and DNA probes for Mycoplasma pneumoniae and Legionella.
Results: In 72 cases (71.3%) some pathogen was found and in 5 cases more than one microorganism was involved. The etiology was bacterial in 31% of the cases, with S. pneumoniae being the most frequent (19 cases). Forty percent of the cases were "atypical" pneumonias with 33 cases of M. pneumoniae and 5 by Chlamydia pneumoniae. Diagnostic data of viral pneumonia were found in 2 cases. DNA probes were not useful for the diagnosis of pneumonia by Legionella pneumophila and had low effectiveness (31.8%) in Mycoplasma pneumoniae CAP.
Conclusions: a) M. pneumoniae was the most frequent pathogen (33%). b) DNA probes for M. pneumoniae had low sensitivity in sputum (31.8%) and none in pharyngeal exudate. c) Acute infection by C. pneumoniae was diagnosed in 5 cases. Previous data of infection were recorded in 60.4% of the patients. d) Bacterial pneumonia (31%) was underestimated due to a low rate of bacteremic cases (7.9%) and the low number of positive cultures with definitive diagnostic value. e) The evolution was good except in two cases (death due to staphylococcal pneumonia with alcohol withdrawal syndrome and multiorganic failure by disseminated chicken-pox).