2.2 Laboratory testing
Specimens of nasopharyngeal swabs from children younger than 2 years old and throat swabs from children 2 years or older were obtained for detection of SARS-CoV-2 nucleic acid using RT-PCR assay. The testing was performed in the clinical laboratory of the Wuhan Children’s Hospital, and the detailed protocol had been described previously.8
Some routine laboratory results were collected from the clinical testing reports, including the complete blood count (CBC), and serum levels of biomarkers such as inflammatory indicators of C-reactive protein (CRP) and procalcitonin (PCT), the coagulation index of D-dimer, the myocardial injury marker of creatine kinase (CK)-MB, the liver function of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP), and the renal function of serum creatinine and blood urea nitrogen (BUN). Co-infections were indicated by available detection results of other pathogens, including serological measurements of mycoplasma pneumoniae (MP) and chlamydia pneumoniae (ChP), immunoglobulin M (IgM) against Epstein-Barr virus (EBV), cytomegalovirus (CMV) and adenovirus (AdV), and nucleic acid testing of influenza A and B viruses in specimens from pharyngeal swabs. Besides, immunological parameters were collected in detail, including total immunoglobulins (IgG, IgA, IgM and IgE), complements (C3 and C4), peripheral blood CD4+ and CD8+ T, B and NK lymphocyte subsets count, and concentration of serum cytokines including interleukin (IL)-2, 4, 6 and 10, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ.