CD40LG and Epstein-Barr virus infection: Among these confirmed cases, the distributions of Epstein–Barr virus (EBV) capsid antigen immunoglobulin M (VCA IgM) and EBV DNA polymerase chain reaction (PCR) test results were as follows: 1842 patients (69.25%) were positive for both VCA IgM and PCR, indicating a typical acute EBV infection; 557 patients (20.94%) were PCR-positive but VCA IgM-negative; and 261 patients (9.81%) were PCR-negative but VCA IgM-positive.