Etiological Diagnosis of Bacterial Pneumonia by Gram Stain and Quantitative Culture of Expectorates: Leukocytes or Alveolar Macrophages as Indicators of Sample Representativity

Abstract

Sputum samples from 151 patients admitted to Roslagstull Hospital for Infectious Diseases, Stockholm, Sweden, from September 1978 through May 1979 with acute community-acquired lower respiratory tract disease and roentgenological evidence of acute pneumonia were examined by direct microscopy of Gram-stained smears and semiquantitative culture. It was carefully noted if the specimen was collected before or after initiation of antibiotic therapy. For an estimate of the suitability of the samples for bacteriological examination, 2 criteria were applied: presence of alveolar macrophages and purulence, i.e., ratio leukocytes/squamous epithelial cells > 5. The latter was a good indicator of sample suitability; the presence of macrophages was not. Of the 266 samples examined, 76% were deemed purulent. Potentially pathogenic bacteria in numbers of .gtoreq. 105 colony forming units/ml were found in 67% of the purulent sputum samples obtained before antibiotic therapy but in only 36% if such treatment had already been started. Pneumococci were isolated from 52% of pre-treatment samples but from only 8% after treatment. Haemophilus influenzae was found as often in post-treatment samples (17%) as in pre-treatment ones (15%). Enteric gram-negative rods were found twice as often in post-treatment samples (11 vs. 6%). The use of Gram-stained smears was a valuable aid in the interpretation of the culture results and the results could be made available to the clinician within minutes after receipt of the specimen. Staining results agreed with culture results for .apprx. 75% of the purulent samples.