Association Between Pre-Admission 48-Hour Fever Burden and Outcomes in Pediatric Mycoplasma Pneumoniae Infection.

Background: Refractory and severe evolution complicate pediatric Mycoplasma pneumoniae pneumonia (MPP), yet early risk stratification still relies largely on single-time admission biomarkers. We tested whether a prespecified 48-hour pre-admission fever-burden index (FBI48) predicts in-hospital outcomes and improves model performance beyond guideline-consistent clinical and laboratory predictors. Methods: We conducted a retrospective single-center cohort study of hospitalized children ≤14 years with laboratory-confirmed MPP. FBI48 was defined as the area under the temperature-time curve above 38.0 °C over -48 to 0 h (°C·h). Thresholds of 38.5 °C and 39.0 °C were evaluated in sensitivity analyses. Prespecified covariates, chosen based on prior RMPP/SMPP studies and pediatric CAP/MPP guidelines, included age, illness days, SpO2, imaging severity, prior macrolide exposure, antipyretic and steroid use, LDH, log2-transformed NLR, CRP, and PCT. Penalized logistic regression generated predicted risks, while unpenalized models provided adjusted odds ratios. Model performance (AUC, Brier score, calibration) and decision-curve analysis (DCA) net benefit were assessed for base (clinical + laboratory) and augmented (base + FBI48) models across 10-30% risk thresholds. Results: Of 720 eligible hospitalizations, 648 were analyzed. The composite endpoint (RMPP and/or incident SMPP) occurred in 176/648 (27.2%; RMPP 24.7%; SMPP 8.0%). FBI48 was independently associated with the composite endpoint (adjusted odds ratio [aOR] 1.45, 95% CI 1.25-1.68 per 1 SD ≈22 °C·h) and with SMPP alone (aOR 1.58, 95% CI 1.21-2.06). Adding FBI48 to the base model improved AUC from 0.78 to 0.83 (ΔAUC 0.05, p<0.001), reduced the Brier score (0.176 to 0.164, p=0.006), and increased net benefit compared with the base model and a treat-none strategy across 10-30% thresholds. Alternative fever thresholds (38.5 °C/39.0 °C) yielded similar effect sizes. Conclusions: A simple 48-hour pre-admission fever-burden metric provides independent and incremental prognostic information on the risk of refractory or severe evolution in pediatric MPP, complementing guideline-based clinical and laboratory predictors and supporting admission-time risk stratification. External validation and prospective evaluation of dynamic, in-hospital updating are warranted.