Clinical Utility of Intracellular Organisms in Gram-Stained Sputum Among Patients With Methicillin-Resistant Staphylococcus aureus Pneumonia.

INTRODUCTION: Sputum cultures may detect bacteria that are not the true causative pathogens of pneumonia. Gram-stained sputum has demonstrated utility in the diagnosis and treatment of pneumonia. Gap statement: However, the clinical significance of intracellular organisms (ICOs) observed in Gram-stained sputum has not been fully elucidated. AIM: This study aimed to evaluate whether the presence of ICOs morphologically consistent with Staphylococcus species in Gram-stained sputum specimens is associated with the diagnosis of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia and the clinical response to anti-MRSA therapy. METHODOLOGY: A retrospective matched case-control study was conducted between January 2010 and December 2022. Patients who underwent sputum smear and culture testing at Chiba University Hospital were included. RESULTS: Of the 1,075 patients who underwent sputum testing, 65 patients with ICO were identified and matched 1:1 with 65 patients without ICO for analysis. Among these, 30 patients (46.2%) in the ICO-positive group were diagnosed with MRSA pneumonia, compared with 21 patients (32.3%) in the ICO-negative group. The risk difference was 13.9% (bootstrapped 95% CI -3.8% to 30.5%), and the difference was not statistically significant (p = 0.15). Furthermore, among patients with pneumonia, the presence of ICO was not associated with a statistically significant difference in the clinical outcomes of anti-MRSA therapy (p = 0.32; bootstrapped 95% CI, -0.434 to 0.292). CONCLUSION: The presence of ICOs in sputum samples was not significantly associated with MRSA pneumonia and may have limited utility in predicting the clinical response to anti-MRSA therapy.