HLA-DRB1 and Epstein-Barr virus infection: There was significant interaction between HLA-DRB1*1501 positivity and EBV infection based on the additive scale (S = 1.43, 95%CI = 1.05–1.95, P = 0.023; AP = 0.29, 95%CI, 0.12–0.47, P = 0.001; RERI = 1.44, 95%CI, 0.30–2.58, P = 0.013) (Table 2).