Objective To investigate changes in the levels of serum amyloid-A (SAA) and coagulation indicators in children with severe pneumonia complicated by mycoplasma infection and their relationship with the prognosis.

Methods A total of 300 children with severe pneumonia were retrospectively enrolled. All the participants were admitted to the Department of Pediatrics of our hospital and received treatment there between July 2022 and December 2024. The patients were divided into a non–mycoplasma infection group (n = 180) and a mycoplasma infection group (n = 120) according to the presence or absence of mycoplasma infection. Then, children with severe pneumonia complicated by mycoplasma infection were further divided into a favorable prognosis subgroup (n = 85) and a poor prognosis subgroup (n = 35). Demographic and clinical data were collected for all participants. Logistic regression analysis was performed to determine whether age, SAA, fibrinogen (Fib), lung ultrasound (LUS) score, and other variables were influencing factors associated with prognosis, and their diagnostic performance was evaluated using receiver operating characteristic (ROC) curve.

Results The SAA Fib levels and LUS scores of the participants in the mycoplasma infection group were all higher than those in the non-mycoplasma group (all P < 0.05). Spearman correlation analysis showed that serum SAA levels, Fib levels, and LUS scores were positively correlated with both the occurrence of mycoplasma infection and poor prognosis after mycoplasma infection in children with severe pneumonia (all P < 0.05). The ROC curve analysis showed that the combined use of SAA, Fib, and LUS score predicted mycoplasma infection with an area under the curve (AUC) of 0.928 (95% CI, 0.899-0.957). Through multivariate logistic regression analysis, age (odds ratio OR, 0.053; 95% CI, 0.003-0.997), SAA (OR, 1.045; 95% CI, 1.003-1.085), Fib (OR, 1.757; 95% CI, 1.378-8.158), and LUS score (OR, 3.538; 95% CI, 1.480-8.457) were identified as influencing factors associated with prognosis in children with severe pneumonia complicated by mycoplasma infection (all P < 0.05). ROC curve analysis demonstrated that the AUC of age, SAA, Fib, and LUS score for predicting prognosis were 0.837 (95% CI, 0.764-0.856), 0.792 (95% CI, 0.701-0.884), 0.755 (95% CI, 0.655-0.909), and 0.917 (95% CI, 0.828-1.000), respectively. The combined model incorporating the 4 parameters achieved an AUC of 0.997 (95% CI, 0.992-1.000).

Conclusion Age, SAA, Fib, and LUS scores can be used as diagnostic indicators for assessing the prognosis of children with severe pneumonia complicated by mycoplasma infections. The combined model demonstrates the highest predictive performance and may contribute to improved clinical prognostic assessment.