CD40LG and scrub typhus: The absence of information about IgM positivity from the general population, and the probability of high background antibody levels in areas to which scrub typhus is endemic, led us to conduct an unmatched case–control study in which we compared IgM and IgG seropositivity for Orientia tsutsugamushi, the causative agent of scrub typhus, in AES patients and healthy controls.