Clinical utility of intracellular organisms in Gram-stained sputum in patients with methicillin-resistant Staphylococcus aureus pneumonia.

Introduction: Sputum cultures may detect bacteria that are not the true causative pathogens of pneumonia. In the diagnosis and treatment of pneumonia, Gram-stained sputum has demonstrated its utility. Gap statement: However, the clinical significance of intracellular organisms (ICO) observed in Gram-stained sputum has not been fully elucidated. Aim: This study aimed to evaluate whether the presence of intracellular organisms (ICO) morphologically consistent with Staphylococcus species in Gram-stained sputum specimens is associated with MRSA pneumonia diagnosis and 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 culture testing at Chiba University Hospital were included in the study. Results: Of 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%) with ICO positivity were diagnosed with MRSA pneumonia, while 21 patients (32.3%) with ICO negativity were diagnosed with MRSA pneumonia. The risk difference was 13.9% (bootstrapped 95% confidence interval [CI], −3.8% to 30.5%), and this difference was not statistically significant (p = 0.15). Furthermore, in cases of pneumonia, the presence of ICO did not yield a statistically significant difference in the clinical outcome of anti-MRSA medications (p = 0.32, bootstrapped 95% CI [-0.434, 0.292]). Conclusion: The presence of ICO in sputum samples was not significantly associated with MRSA pneumonia and may have limited utility in predicting clinical response to anti-MRSA therapy.