Three studies evaluated herpes simplex virus (HSV) infection in conjunction with CMV infection. In one study, HSV was isolated in the bronchial aspirate of 8 of 25 patients (32%) consisting of six of eight patients with CMV reactivation and 2 of 17 patients without CMV infection (P = 0.004) [16] . In other studies, none or only one patient developed co-infection of CMV and HSV, therefore, the association between CMV and HSV could not be evaluated [8, 17] .