EBV has been implicated as a possible etiologic agent. Several case control studies suggest that there are somewhat higher titers in cases than controls. The problem is that because HD is rare, one has to look at HD cases who have had disease for a long time. The disease itself could affect the likely hood of being exposed, though contact in the health care s system. The immunologic difficulties may also increase the likelihood of raised titers. Also, the problem is that a large percentage of people will have raised titers, thus it is not very specific. Despite all this, there appears to be an association, although it is weak.