HLA-DRB1 and infection: We found an odds ratio for this combination (OR=3.17, 95% CI=1.65–5.80) that exceeds that for HLA-B*15:01 alone, suggesting that while not significantly associated with the asymptomatic infection on its own in this cohort, the class II allele HLA-DRB1*04:01 enhances the effect of HLA-B*15:01.