Correlation Of Sputum Gram’s Stain And Culture In Lower Respiratory Tract Infections

Abstract

Background: For diagnosis of Lower respiratory tract infections (LRTIs), expectorated sputum is the most commonly received sample in the laboratory. Normal resident bacteria of the oropharynx usually contaminate the sputum sample. The value of sputum microscopy and culture in the diagnosis, management and outcome of LRTIs is a matter of controversy. The following study was conducted to evaluate the correlation of Gram's stain and culture in sputum samples from LRTIs. Materials & Methods: The present study was during a one year period (January to December 2012). A total of 120 sputum samples were processed . All the samples were processed through Gram's stain and culture. The Gram's smear was examined for the presence of polymorphs, epithelial cells and bacterial forms. Sputum samples were evaluated based on Bartlett's grading system. The cultures were incubated at 37 0 C overnight and identified in a Microscan autoSCAN 4 instrument (SIEMENS). Results And Conclusions: Out of 120 sputum samples processed, 78 (65%) were acceptable and 42 (35%) were not meeting the standard criteria of Bartlett. Potential pathogens were obtained from 70 of 78 acceptable samples (89.74%), and from 4 of 42 non-acceptable samples (9.52%). Gram's stain could detect similar morphological forms as that obtained in culture in 62 of the acceptable samples (sensitivity- 79.48%) and 4 of the non acceptable samples (sensitivity -4.76%). The most common organisms isolated in the present study include: Klebsiella pneumoniae- 22.85%, Streptococcus pneumoniae- 11.49% and Staphylococcus aureus- 10%. As authors of the present study, we recommend initial screening of sputum samples for clinically relevant results, and reject the non-acceptable samples, and re-order for fresh and correct specimens.