Quantitative Culture and Gram Stain of Sputum in Pneumonia1

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 deoxyribonuclease 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. Fifteen of the 17 patients had concentrations of the responsible pathogen of more than 106 organisms per ml. None of the 3 patients with pneumonia due to anaerobes had concentrations of more than 105 aerobic pathogens per ml of sputum. The pathogen that was the presumed cause of pneumonia was present in excess of 106 organisms per ml of secretions in 21 of 33 additional patients. Gram stains of liquefied secretions did not ...