Background. Current guidelines in hematopoietic stem cell transplantation (HSCT) endorse antiviral prophylaxis for all recipients seropositive for varicella-zoster virus. Nonmyeloalative (NMA) regimens have expanded in the past decade, but few data exist in patients undergoing NMA HSCT to support such a recommendation. The objectives of this study were to describe the clinical features, incidence and risk factors for herpes zoster (HZ) in a homogenous cohort of NMA HSCT patients.

Methods. All patients undergoing NMA HSCT at Hôpital Maisonneuve-Rosemont (Canada) between 7/2000-12/2008 were included. Patients received the same conditioning regimen (fludarabine and cyclophosphamide), followed by infusion of blood stem cells from an HLA-identical related donor. Tacrolimus and mycophenolate mofetil were used to prevent graft-vs.-host disease. CMV reactivation was monitored using a preemptive strategy; HSV-seropositive recipients received antiviral prophylaxis.

Results. A total of 179 patients were followed for 33 months (median, IQR: 21-59). HZ developed in 66 patients (37%) at a median of 8.3 months post-HSCT; the incidence rate was 175 cases/1,000 person-years. Thoracic dermatomes were most frequently involved (30%); dissemination occurred in 5 patients. No death resulted from HZ, but 23% developed post-herpetic neuralgia. The estimated cumulative HZ incidence was 27, 36, and 44% at 1, 2, and 3 years respectively. In multivariate analysis, CMV and HSV reactivation appeared protective against HZ (HR= 0.52 and 0.26, respectively).

Conclusion. The incidence of HZ in our study sample is similar to the incidence reported for myeloablative regimens. Antiviral treatment for viral reactivations protects against HZ. Antiviral prophylaxis for HZ for at least the 1^st year post-transplantation, as recommended, would also apply to the NMA HSCT population.