In bone marrow transplant recipients, CMV infection has been linked to acute graft verus host illness. There are multiple genotypes of CMV (gB 1-4), each with slight differences in the gene encoding envelope glycoprotein gB. The relationship between gB types and acute graft versus host illness and death from myelosuppression has been investigated. Torok-Storb et al (1997) observed that gB3 and gB4 were connected to a higher degree of myelosuppression and death when disease type, donor-recipient HLA matching, donor CMV serostatus, and age were taken into account. Although mixed gB genotype infections were connected to greater viral loads and delayed viral clearance, no specific CMV genotypes were linked to a worse outcome in solid organ transplant recipients.