Characteristics of the study subjects
A total of 944 patients with community-acquired pneumonia aged ≥1 year were screened for inclusion in the study. Of these, 135 patients with incomplete data were removed from further analysis, and the remaining 809 patients underwent the study assessments. Among these 809 patients, 508 (62.8%) had a positive MPP PCR result and a significant antibody response, including 78 cases of mixed infection with mycoplasma and other pathogens. After exclusion of mixed infection, a total of 430 patients with MPP were selected for further analysis including 306 GMPP cases and 124 RMPP cases. The mean age of the patients was 4.6±2.5 years, with a male to female ratio of 1.23:1. Most (60.5%) of the RMPP patients were older than 5 years old, and the age group of > 5 years had the highest proportion of both GMPP and MPP cases. The age distribution is shown in Figure1. The RMPP group had a higher mean age than the GMPP group, with a statistically significant difference (P<0.001). No difference was found in the male to female ratio. Hospitalization time, preadmission fever duration and total fever duration were longer in the RMPP group. Moreover, the levels of WBC, CRP, N %, ESR, LDH, ALT, AST and D-D were higher in the RMPP group (all P<0.05; Table 1).
Correlation analysis of D-D level with WBC, CRP, LDH, and ESR
WBC was normal in MPP patients, and it was increased in patients with RMPP, as well as D-D (Table 1), and the D-D level was found to be positively correlated with WBC (Spearman r=0.211, P<0.001). The D-D level was also found to be positively correlated with CRP, LDH, and ESR (Spearman r=0.452, P<0.001; Spearman r=0.448, P<0.001 and Spearman r=0.376, P<0.001, respectively, Table 2).
Predictive value of D-D level for RMPP
Univariate analysis identified 11 variables (age, preadmission fever duration, WBC, N%, L%, CRP, ALT, AST, LDH, ESR and D-D) as significant risk factors (P<0.05, Table 1). The hospitalization time and total fever duration were not included because they were advanced indicators. The 11 variables were put into the multivariate regression model. Multivariate logistic regression identified preadmission fever duration, CRP, LDH and DD as independent risk factors for RMPP after adjustment for confounders (P<0.05, Table 3). The cutoff values for preadmission fever duration, CRP, LDH and D-D were 6.5 days, 18.5mg/L, 339 IU/L, and 738 mg/ml, respectively. D-D was found to have the highest predictive power for RMPP (P<0.001, Figure 2). For D-D levels > 738 ng/ml, the sensitivity and specificity of the prediction for liver injury were 79.8% and 93.5%, respectively.
Predictive value of D-D level for MPP with complications
ROC curve analysis was also performed to further evaluate the value of the D-D level in predicting complications such as atelectasis, pleural effusion, liver injury, skin rash, myocardial damage, pulmonary embolism and mucus plug formation. The results showed that the serum D-D level could robustly predict pleural effusion and liver injury (P<0.001). For D-D levels > 930 ng/ml, the sensitivity and specificity of the prediction for pleural effusion were 80.6% and 60.5%, respectively. For D-D levels > 2100.5 ng/ml, the sensitivity and specificity of the prediction for liver injury were 93.3% and 72.7%, respectively.
Degree of D-D elevation and complications
Levels of D-D were classified as normal, mildly increased, moderately increased, and severely increased. Pleural effusion was the most presence complication across the four classifications, The incidence of pleural effusion increased with increasing D - D levels and differed significantly among the normal, mild increase, and moderate increase groups (P<0.01); however, the difference between the moderate increase group and the severe increase group was not statistically significant (P>0.05; Figure3). The incidence of atelectasis was significantly higher in the group with mildly elevated D-D levels than in the normal group (P<0.01) but did not further increase with increasing D-D levels (moderately elevated group, P=0.622; severely elevated group, P=0.421). Only one cases of pulmonary embolism were found in our study, who was with a lower right pulmonary artery (D-D=2401 ng/ml) and discharged without complications. She was currently in good health by follow-up.
Serum D-D level after treatment for one week
A total of 74 children were reviewed for D-D level, WBC, and CRP after treatment for one week, including 5 patients with GMPP and 69 patients with RMPP. After treatment, the levels of WBC and CRP in most children were reduced to normal (63.0% and 81.5%, respectively). In both the GMPP and RMPP groups, the D-D level decreased significantly with treatment (P<0.05, Table 4), although 91.4% of children had D-D levels that remained above the upper limit of normal (>280 ng/ml), and 27.1% of children had a moderate-to-severe increase in D-D, all of which were within the RMPP group. According to the D-D level after a further one-week interval, patients were divided into a normal group and an abnormal group. More pleural effusions were observed in the abnormal group than in the normal group (67.2% and 28.6%, respectively, P=0.04).
Serum D-D level and mucus plug formation
A total of 77 MPP patients received bronchoscopy, and 28 cases (36.4%) had mucus plug formation under bronchoscopy. There was statistically significant difference in D-D level between the bronchoscope group and the non-bronchoscope group (P<0.001). However, there was no statistically significant difference in D-D level between the mucous plug group and the nonmucous plug group (P=0.093).