Utility of Gram stain in evaluation of sputa from patients with cystic fibrosis

Abstract

The utility of sputum Gram stain in assessing salivary contamination and in predicting the presence of pathogens on the basis of morphology was investigated in 287 respiratory specimens from patients with cystic fibrosis. Where acceptability for culture was defined as a leukocyte/squamous epithelial cell ratio of >5, 76.6% (220 of 287) of respiratory specimens received in the laboratory were considered acceptable. Unacceptable specimens were more common in younger patients. The positive predictive value of the Gram stain for growth from acceptable sputum samples was 98% for Pseudomonas aeruginosa, 84.4% for Pseudomonas cepacia, 86.3% for Staphylococcus aureus, and 100% for Haemophilus influenzae. In cystic fibrosis patients, as has been reported for respiratory specimens in general, Gram stain of respiratory specimens is helpful for interpreting culture results.