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

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.

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.

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.

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).

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.