QUANTITATIVE CULTURE AND GRAM STAIN OF SPUTUM IN PNEUMONIA

Abstract

The etiologic diagnosis of fever and pulmonary disease may be difficult because many bacteria, some of which are potentially pathogenic, are found in the oropharynx. The solution to this problem was sought by determining the number of potentially pathogenic aerobic bacteria in respiratory secretions of 194 adult patients, 53 of whom had bacterial pneumonia. Liquefaction of secretions with DNase and acetylcysteine, followed by aerobic culture of 10-3 and 10-5 dilutions, correctly identified the cause of pneumonia in 17 patients in whom the etiology was proved by other means. Of the 17 patients, 15 had concentrations of the responsible pathogen or more than 106 organisms/ml. None of the 3 patients with pneumonia due to anaerobes had concentrations of more than 105 aerobic pathogens/ml of sputum. The pathogen that was the presumed cause of pneumonia was present in excess of 106 organisms/ml of secretions in 21 of 33 additional patients. Gram stains of liquefied secretions did not predict the etiology of the pneumonia ultimately determined. Cultures that were performed in the routine manner correlated with the etiology of pneumonia in only 60% of the patients studied, and 27 of 61 such cultures (44%) from patients without pneumonia contained reportable pathogens. The sensitivity and specificity of the quantitative culture technique were good for pneumonia that was due to aerobic bacteria, was acquired outside the hospital and was not associated with bronchiectasis. The specificity was not good for gram-negative bacillary pneumonia acquired in the hospital or by patients who had bronchiectasis.