CD40LG and infection: At the same time, due to the different time intervals of MP-RNA and MP-Ab detection from onset to hospitalization in different children, we divided the detection time intervals into four groups: ≤ 7 days, 8 ~ 14 days, 15 ~ 30 days, and > 30 days, according to the characteristics that IgM antibody generally appeared 4–5 days after infection and reached the peak time point in 3–4 weeks.