Resistant herpes simplex virus type 1 infection: An emerging concern afterallogeneic stem cell transplantation

Fourteen cases of severe acyclovir-resistant herpes simplex virus type I (H SV-1) infection, 7 of which showed resistance to foscarnet, were diagnosed among 196 allogeneic stem cell transplant recipients within a 29-month peri od. Recipients of unrelated stem cell transplants were at higher risk. All patients received foscarnet; 8 subsequently received cidofovir, Strains wer e initially foscarnet-resistant in 3 patients and secondarily so in 4 patie nts. In vitro resistance to acyclovir or foscarnet was associated with clin ical failure of these drugs; however, in vitro susceptibility to foscarnet was associated with complete response in only 5 of 7 patients. No strain fr om any of the 7 patients was resistant in vitro to cidofovir; however, only 3 of 7 patients achieved complete response. Therefore, acyclovir- and/or f oscarnet-resistant HSV-1 infections after allogeneic stem cell transplantat ion have become a concern; current strategies need to be reassessed and new strategies must be evaluated in this setting.