Etiology of community-acquired pneumonia. Evaluation by transtracheal aspiration, blood culture, or serology.

In a 5-year period, 254 patients with community-acquired pneumonia were attended to. Transtracheal aspiration (TTA) could be performed on 119 patients, blood cultures were performed on 201 patients, and 74 patients underwent serologic examinations. By use of these procedures, an etiologic diagnosis was established in 93 cases. Streptococcus pneumoniae was the most common pathogen as it was found in 35 cases. Eleven of these 35 patients (31.4 percent) had pneumococcemia, and the mortality in this group was 27.3 percent. None of the patients with pneumococcal pneumonia and negative blood culture died. Haemophilus influenzae was the only isolated pathogen from transtracheal aspirated sputum in 16 cases and accounted for 17.5 percent of pneumonias in previous healthy individuals under 50 years of age. Mycoplasma pneumonia infections, Legionella pneumophila infections, and Chlamydia infections were found in ten, eight, and three cases, respectively. The overall agreement between microscopy and culture of respiratory secretions obtained by TTA was 58.8 percent, and microscopy can be a guide when choosing the initial antibiotic treatment. No statistically significant difference in the rate of isolating bacteria among patients treated with antibiotics prior to TTA and patients not previously treated with antibiotics was seen. When contraindications were respected, we found TTA to be a safe procedure.