Usefulness of sputum gram stain for etiologic diagnosis in community-acquired pneumonia: a systematic review and meta-analysis

BACKGROUND: Implementation of sputum Gram stain in the initial assessment of community-acquired pneumonia (CAP) patients is still controversial. We performed a systematic review and meta-analysis to investigate the usefulness of sputum Gram stain for defining the etiologic diagnosis of CAP in adult patients. METHODS: We systematically searched the Medline, Embase, Science Direct, Scopus and LILACS databases for full-text articles. Relevant studies were reviewed by at least three investigators who extracted the data, pooled them using a random effects model, and carried out quality assessment. For each bacterium (Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, and Gram-negative bacilli), pooled sensitivity, specificity, positive and negative likelihood ratios were reported. RESULTS: After a review of 3539 abstracts, 20 articles were included in the present meta-analysis. The studies included yielded 5619 patients with CAP. Pooled sensitivity and pooled specificity of sputum Gram stain were 0.59 (95% CI, 0.56–0.62) and 0.87 (95% CI, 0.86–0.89) respectively for S. pneumoniae, 0.78 (95% CI, 0.72–0.84) and 0.96 (95% CI, 0.94–0.97) for H. influenzae, 0.72 (95% CI, 0.53–0.87) and 0.97 (95% CI, 0.95–0.99) for S. aureus, and 0.64 (95% CI, 0.49–0.77) and 0.99 (95% CI, 0.97–0.99) for Gram-negative bacilli. CONCLUSION: Sputum Gram stain test is sensitive and highly specific for identifying the main causative pathogens in adult patients with CAP. TRIAL REGISTRATION: This study has been registered at PROSPERO International prospective register of systematic reviews under registration no. CRD42015015337. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12879-019-4048-6) contains supplementary material, which is available to authorized users.