In our study, based on the kinetics of anti-CMV IgG (Table2), the seroconversion of anti-CMV IgM (Table3) and the results of CMV IgG avidity assay in children with longitudinal sera, we concluded that primary CMV infection in children mainly occurred before 3.5 months of age, which is earlier than the infection age identified before in developing countries[13,17]. Here, CD40LG is linked to infection.