Validation of sputum Gram stain for treatment of community-acquired pneumonia and healthcare-associated pneumonia: a prospective observational study

Abstract

Background: The usefulness of sputum Gram stain in patients with community-acquired pneumonia (CAP) is controversial. There has been no study to evaluate the diagnostic value of this method in patients with healthcare-associated pneumonia (HCAP). The purpose of this study was to evaluate the usefulness of sputum Gram stain in etiological diagnosis and pathogen-targeted antibiotic treatment of CAP and HCAP.

Methods: We conducted a prospective observational study on hospitalized patients with pneumonia admitted to our hospital from August 2010 to July 2012. Before administering antibiotics on admission, Gram stain was performed and examined by trained physicians immediately after sputum samples were obtained. We analyzed the quality of sputum samples and the diagnostic performance of Gram stain. We also compared pathogen-targeted antibiotic treatment guided by sputum Gram stain with empirical treatment.

Results: Of 670 patients with pneumonia, 328 were CAP and 342 were HCAP. Sputum samples were obtained from 591 patients, of these 478 samples were good quality. The sensitivity and specificity of sputum Gram stain were 62.5% and 91.5% for Streptococcus pneumoniae, 60.9% and 95.1% for Haemophilus influenzae, 68.2% and 96.1% for Moraxella catarrhalis, 39.5% and 98.2% for Klebsiella pneumoniae, 22.2% and 99.8% for Pseudomonas aeruginosa, 9.1% and 100% for Staphylococcus aureus. The diagnostic yield decreased in patients who had received antibiotics or patients with suspected aspiration pneumonia. Pathogen-targeted treatment provided similar efficacy with a decrease in adverse events compared to empirical treatment.

Conclusions: Sputum Gram stain is highly specific for the etiologic diagnosis and useful in guiding pathogen-targeted antibiotic treatment of CAP and HCAP.

Figure 1

Bacterial morphotypes in sputum Gram stain (×100, oil immersion field). Gram positive diplococci (lancet-shaped or football-shaped) are suggestive of Streptococcus pneumoniae (A). Cluster of Gram positive cocci are suggestive of Staphylococcus aureus (B). Tiny Gram negative coccobacilli are suggestive of Haemophilus influenzae (C). Gram negative diplococci (kidney bean-shaped) are suggestive of Moraxella catarrhalis (D). Plump Gram negative rods are suggestive of Klebsiella pneumoniae (E). Thin gram negative rods are suggestive of Pseudomonas aeruginosa (F).

Figure 2

Results of sputum Gram stain in patients with CAP and HCAP.