Comparison of immune and inflammatory markers among groups
IgA, IgG, and IgM levels were lower in the severe group than in the mild-to-moderate group and were lower in the mild-to-moderate group than in the control group. CRP showed the opposite pattern. Pairwise differences were statistically significant (P < 0.05; Table 1).
Comparison of immune and inflammatory markers between prognostic groups
Among children with severe MPP, IgA, IgG, and IgM levels were lower, and CRP levels were higher in the poor-prognosis group than in the good-prognosis group (all P < 0.05; Table 2).
Discriminative ability of individual immune and inflammatory markers
The AUCs for IgA, IgG, IgM, and CRP were 0.788 (95% CI, 0.659–0.885), 0.707 (95% CI, 0.571–0.820), 0.696 (95% CI, 0.560–0.811), and 0.796 (95% CI, 0.668–0.891), respectively. The corresponding cutoff values were 1.10 g/L, 8.35 g/L, 1.21 g/L, and 51.05 mg/L. Sensitivity and specificity are presented in Table 3. These individual ROC analyses were exploratory. The corresponding ROC curves are shown in Figure 1.
Univariate analysis of factors associated with prognosis
Fever duration, lesion type, immune dysfunction, CRP >51.05 mg/L, and extrapulmonary complications differed significantly between the good- and poor-prognosis groups (all P < 0.05). Age, sex, and lesion location did not differ significantly between the groups (all P > 0.05; Table 4).
Multivariate logistic regression analysis of prognostic factors
Poor prognosis was entered as the dependent variable. Fever duration, lesion type, immune dysfunction, CRP >51.05 mg/L, and extrapulmonary complications were entered as candidate independent variables. Lesion type was coded as 1 for a large patchy shadow and 0 for a patchy or flocculent shadow; immune dysfunction and extrapulmonary complications were coded as 1 when present and 0 when absent; and CRP was coded as 1 for >51.05 mg/L and 0 for ≤51.05 mg/L. Immune dysfunction (OR, 2.061; 95% CI, 1.518–2.798; P < 0.001) and extrapulmonary complications (OR, 1.732; 95% CI, 1.374–2.182; P < 0.001) remained independently associated with poor prognosis in the exploratory multivariable analysis (Table 5).
DATA AVAILABILITY:
The de-identified raw data underlying this study are publicly available in Figshare at https://doi.org/10.6084/m9.figshare.33155195.

Figure 1: Receiver operating characteristic (ROC) curves of individual biomarkers for predicting poor prognosis in children with severe Mycoplasma pneumoniae pneumonia. ROC curves were generated separately for serum immunoglobulin A (IgA), immunoglobulin G (IgG), immunoglobulin M (IgM), and C-reactive protein (CRP). The y-axis represents sensitivity, and the x-axis represents 1 − specificity. The diagonal line indicates the reference line (AUC = 0.5). Areas under the curve (AUCs) with 95% confidence intervals are shown in the figure. The ROC analyses were performed as exploratory assessments of each biomarker's discriminative ability. Please click here to view a larger version of this figure.
| Group | Number of cases | IgA (g/L) | IgG (g/L) | IgM (g/L) | CRP (mg/L) |
| Severe group | 114 | 0.95 ± 0.31 b | 8.45 ± 1.06 b | 1.24 ± 0.55 b | 49.92 ± 6.25 b |
| Mild to moderate group | 58 | 1.28 ± 0.40 a | 8.97 ± 1.23 a | 1.53 ± 0.63 a | 30.37 ± 6.10 a |
| Control group | 40 | 2.63 ± 0.36 ab | 10.82 ± 1.38 ab | 2.41 ± 0.69 ab | 9.80 ± 4.49 ab |
| F | | 350.852 | 60.599 | 56.208 | 730.412 |
| P | | < 0.001 | < 0.001 | < 0.001 | < 0.001 |
Table 1: Comparison of serum immunoglobulin and C-reactive protein levels among the severe Mycoplasma pneumoniae pneumonia (MPP), mild-to-moderate MPP, and healthy control groups. Values are presented as mean ± standard deviation (SD). One-way analysis of variance was used for group comparisons. aP < 0.05 versus the severe MPP group; bP < 0.05 versus the mild-to-moderate MPP group.
| Group | Number of cases | IgA (g/L) | IgG (g/L) | IgM (g/L) | CRP (mg/L) |
| Good prognosis | 75 | 1.12 ± 0.36 | 8.76 ± 1.12 | 1.35 ± 0.62 | 41.89 ± 5.20 |
| Poor prognosis | 39 | 0.63 ± 0.22 | 7.85 ± 0.94 | 1.03 ± 0.42 | 65.36 ± 8.27 |
| t | | 7.77 | 4.339 | 2.893 | 18.551 |
| P | | < 0.001 | < 0.001 | 0.005 | < 0.001 |
Table 2: Comparison of serum immunoglobulin and C-reactive protein levels between children with good and poor prognosis among those with severe Mycoplasma pneumoniae pneumonia. Values are presented as mean ± SD. Comparisons were performed using the independent-samples t-test.
| Index | Critical value | AUC | Sensitivity | Specificity | 95 % CI | P |
| IgA (g/L) | 1.10 | 0.788 | 59.5 | 95 | 0.659–0.885 | < 0.001 |
| IgG (g/L) | 8.35 | 0.707 | 70.2 | 70 | 0.571–0.820 | 0.001 |
| IgM (g/L) | 1.21 | 0.696 | 59.5 | 75 | 0.560–0.811 | 0.006 |
| CRP (mg/L) | 51.05 | 0.796 | 75.7 | 80 | 0.668–0.891 | < 0.001 |
| Joint testing | | 0.920 | 91.8 | 80 | 0.817–0.975 | < 0.001 |
Table 3: Receiver operating characteristic (ROC) analysis of individual biomarkers for predicting poor prognosis in children with severe Mycoplasma pneumoniae pneumonia. The table summarizes the optimal cutoff values, area under the curve (AUC), sensitivity, specificity, 95% confidence intervals (CIs), and P-values for IgA, IgG, IgM, and CRP.
| Clinical information | Good prognosis (n = 75) | Poor prognosis (n = 39) | χ 2 / t | P |
| gender | male | 42 (56.00) | 24 (61.54) | 0.323 | 0.570 |
| female | 33 (44.00) | 15 (38.46) | | |
| age) | | 7.34 ± 2.36 | 6.96 ± 2.82 | 0.762 | 0.448 |
| Thermal range (d) | | 4.63 ± 1.22 | 7.85 ± 2.34 | 9.676 | < 0.001 |
| Lesion type | Spotty, flocculent shadows | 52 (69.33) | 10 (25.64) | 19.745 | < 0.001 |
| Large patchy shadows | 23 (30.67) | 29 (74.36) | | |
| Lesion | Left upper lobe | 14 (18.67) | 8 (20.51) | 1.056 | 0.788 |
| Left lower lobe | 23 (30.67) | 14 (35.90) | | |
| Right upper lobe | 16 (21.33) | 9 (23.08) | | |
| Right lower lobe | 22 (29.33) | 8 (20.51) | | |
| Immune dysfunction | yes | 15 (20.00) | 32 (82.05) | 40.772 | < 0.001 |
| no | 60 (80.00) | 7 (17.95) | | |
| C RP | > 51.05 mg /L | 14 (18.67) | 26 (66.67) | 25.955 | < 0.001 |
| < 51.05 mg /L | 61 (81.33) | 13 (33.33) | | |
| Extrapulmonary complications | have | 12 (16.00) | 28 (71.79) | 35.069 | < 0.001 |
| none | 63 (84.00) | 11 (28.21) | | |
Table 4: Univariate analysis of clinical characteristics associated with prognosis in children with severe Mycoplasma pneumoniae pneumonia. Continuous variables are presented as mean ± SD, and categorical variables are presented as n (%). Group comparisons were performed using the independent-samples t-test or the chi-square (χ2) test, as appropriate.
| Risk factors | Beta value | SE value | w ald 2 | 95 % CI | OR | P |
| Immune dysfunction | 0.723 | 0.156 | 21.48 | 1.518–2.798 | 2.061 | < 0.001 |
| Extrapulmonary complications | 0.549 | 0.118 | 21.646 | 1.374–2.182 | 1.732 | < 0.001 |
Table 5: Exploratory multivariable logistic regression analysis of factors associated with poor prognosis in children with severe Mycoplasma pneumoniae pneumonia. Regression results are presented as regression coefficients (β), standard errors (SE), Wald χ2 statistics, odds ratios (ORs), 95% confidence intervals (CIs), and P values. Immune dysfunction and extrapulmonary complications remained independently associated with poor prognosis in the exploratory multivariable analysis.
Supplementary File 1: Cohort dataset and variable dictionary. This supplementary file contains the de-identified study dataset (Cohort_Data) and the accompanying variable dictionary, including variable definitions, coding rules, data types, and availability for all study variables used in the analyses.Please click here to download this file.