A prospective study of the diagnostic utility of sputum Gram stain in pneumonia

Introduction: Sputum Gram stain and culture have been said to be unreliable indicators of the microbiological diagnosis of bacterial. pneumonia. The etiological diagnosis of pneumonia is surrounded by great degree of uncertainty. This uncertainty should be and can be calculated and incorporated in the diagnosis and treatment. Study objectives: To determine the diagnostic accuracy and diagnostic value of sputum Gram stain in etiological diagnosis and initial selection of antimicrobial therapy of bacterial community acquired pneumonia (CAP). Design-Method: Prospective study of 1390 patients with CAP admitted January 2002-June 2008, to our institutions. Of the 1390 patients, 178 (12.8%) fulfilled the criteria for inclusion into this study (good-quality sputa and presence of the same microorganism in blood and sputum cultures which was used as gold standard for assessing the diagnostic accuracy and diagnostic value of sputum Gram stain). Results: The sensitivity of sputum Gram stain was 0.82 for Pneumococcal pneumonia, 0.76 for Staphylococcal pneumonia, 0.79 for Haemophilus influenzae pneumonia and 0.78 for Gram-negative bacilli pneumonia. The specificity of sputum Gram stain was 0.93 for Pneumococcal pneumonia, 0.96 for Staphylococcal pneumonia, 0.96 for H. influenzae pneumonia and 0.95 for Gram-negative bacilli pneumonia. The positive likelihood ratio (LR+) was 11.58 for Pneumococcal pneumonia, 19.38 for Staphytococcal pneumonia, 16.84 for H. influenzae pneumonia, 14.26 for Gram-negative bacilli pneumonia. The negative likelihood ratio (LR-) was 0.20 for Pneumococcal pneumonia, 0.25 for Staphylococcal pneumonia, 0.22 for H. influenzae pneumonia, and 0.23 for Gram-negative bacilli pneumonia. Conclusions: Sputum Gram stain is a dependable diagnostic test for the early etiological diagnosis of bacterial CAP that helps in choosing orthological and appropriate initial antimicrobial therapy. (C) 2009 The British Infection Society. Published by Elsevier Ltd. All rights reserved.