Demographics and Clinical Feature Analysis of the Children with COVID-19
During the study period, a total of 490 children with confirmed or suspected COVID-19 were hospitalized at our hospital; among them, 121 children with complete clinical data were included in this study. The median age was 6.0 years (range: 0.13–15.0 years). There were 82 boys (67.8%) and 39 girls (32.2%). There were 101 mild (83.5%, asymptomatic infection, and mild and common cases), 12 severe (9.9%), and 8 critical (6.6%) cases.
Upon admission, the children’s symptoms mainly included fever (78 cases, 64.5%) and cough (69 cases, 57.0%); minor symptoms included gastrointestinal symptoms (13 cases, 10.7%), nasal discharge (11 cases, 9.1%), sputum (11 cases, 9.1%), fatigue (9 cases, 7.4%), respiratory distress (9 cases, 7.4%), headache (6 cases, 5.0%), chest distress (5 cases, 4.1%), and muscle soreness (4 cases, 3.3%). Eighty-five patients (70.2%) tested positive for SARS-CoV-2 nucleic acid on admission; 97 patients (80.2%) had radiological changes in the lungs, with typical radiological changes of ground-glass opacities in both lungs; 85 children (70.2%) were confirmed cases, and 36 children (29.8%) were suspected cases.
The clinical symptoms of the children in groups I and II were relieved after treatment, and all were discharged after meeting the criteria of cure. The median lengths of hospital stay of the children in groups I and II were 11.0 days (IQR: 9.0–14.0 days) and 10.0 days (IQR: 8.75–12.5 days), respectively. The length of hospital stay between the two groups was not significantly different (P = 0.9). As of March 16, 2020, 2 patients in group III were still hospitalized, and 1 patient in group III died 36 days after admission, with a median hospital stay of 20.5 days (IQR: 17.25–35.25 days). There was no progression from mild to severe or from severe to critical cases among the hospitalized children.
Analysis of the Peripheral Blood Indices of the Children Infected with SARS-CoV-2
The Kruskal–Wallis test and Spearman correlation analysis of the initial laboratory examinations on admission (Table 2, Figures 1A) of the 121 children showed that there was a significant decrease from groups I to III in CD3+CD4+ Th cell (P < 0.001), CD3+CD8+ Tc cell (P < 0.001), and CD16+CD56+ NK cell (P = 0.001) counts. Groups II and III had significantly lower CD19+ B cell counts than group I (P = 0.026). Group III had a significantly higher Th/Tc cell ratio than groups I and II (P = 0.027).
From group I to III, there was a significant increase in IL-6, IL-10, and IFN-γ (Table 2, Figure 1B), and FERR, SAA, and PCT (Table 2, Figure 2), i.e., with increasing disease severity (P < 0.001). Although CRP was significantly higher in groups II and III than in group I (P < 0.001), its highest mean value was highest (36.0 ± 32.9 mg/L) in group II.
The results of routine blood testing on admission showed a decrease from group I to III for hemoglobin (P < 0.001), red blood cell count (P < 0.001), and eosinophil count (P = 0.008). Groups II and III had significantly lower lymphocyte counts than group I (P = 0.001), with group II having the lowest count. Other routine blood parameters between the three groups were not significantly different (Table 2).
Prognostic Factors for Early Identification of Critical COVID-19
Next, we explored the possibility of early identification of children with critical COVID-19 using the above peripheral blood parameters as prognostic factors. PCA using the R package factoextra revealed a clear difference between the three groups, with more significant differences between groups I+II and group III (Figure 3A). Therefore, groups I and II were combined into group A, and group III was designated group B for PCA and comparisons (Figure 3B).
A comprehensive analysis of the contributory values suggested that 10 indices (red blood cells [RBC], hemoglobin [Hb], lymphocytes [Lym], T lymphocytes [T], Th cells [Th], Tc cells [Tc], B lymphocytes [B], IL-6, IL-10, IFN-γ) can be used as potential prognostic factors, and further statistical analysis was performed on these indices.
To determine the diagnostic value of the above 10 indices, we calculated the AUC of the ROC curve. The AUC values of T (0.944), RBC (0.941), Tc (0.935), IL-10 (0.93), Hb (0.927), Th (0.925), and IL-6 (0.898) were greater than that of Lym (0.718), B (0.708), and IFN-γ (0.688). Meanwhile, the cutoff values for T (875.5), RBC (4.195), Tc (348.5), IL-10 (6.08), Hb (117.5), Th (415.0), IL-6 (15.39), Lym (1.77), B (342.0), and IFN-γ (4.24) were calculated according to the Youden index of the ROC curve. T, Th, Tc, IL-6, IL-10, RBC, and Hb had AUC values of >0.85, indicating that they contributed significantly to the identification of critical cases in this study.