Novel inflammatory biomarkers and disease severity in hospitalized children with Mycoplasma pneumoniae pneumonia: a retrospective study

Background: A resurgence of Mycoplasma pneumoniae (M. pneumoniae) infections has been observed worldwide, including large outbreaks in China during 2023–2024, with a higher incidence of severe and complicated pneumonia cases. Identifying clinical and laboratory indicators associated with disease severity may assist clinicians in early risk stratification. This study aimed to explore the association between novel inflammatory biomarkers and disease severity in hospitalized children with M. pneumoniae pneumonia (MPP).

Methods: We conducted a retrospective analysis of 866 hospitalized children with MPP. For each case, we calculated the neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), and systemic inflammation response index (SIRI). Multivariable logistic regression analysis was performed to identify factors associated with severe MPP. Receiver operating characteristic (ROC) curves were used to evaluate the discriminatory performance of these biomarkers for distinguishing severe cases from non-severe MPP.

Results: Compared with the non-severe group, children with severe MPP showed significantly higher levels of NLR, PLR, and SII (all P<0.001), whereas SIRI levels were lower (P=0.01). Patients with severe MPP were also older and had longer fever duration (P<0.001). In ROC analysis, SII demonstrated limited discriminatory ability for identifying severe MPP. The combination of SII and fever duration showed the highest area under the curve (AUC) among the evaluated indices.

Conclusions: Elevated SII and prolonged fever duration were associated with increased disease severity in children with MPP. Although the discriminatory performance of SII alone was limited, inflammatory indices may provide additional information for clinical risk stratification when interpreted alongside clinical features. Further prospective studies are needed to validate these findings.