Factors contributing to the risk of cytomegalovirus infection in patients receiving renal transplants.

Following renal transplantation, the incidence of CMV infection varies from 52% (18) to 91% (2). There are a number of putative risk factors which contribute to cytomegalovirus infection after transplantation (Table 1). It is not clear how important each one is. The virus may either be introduced from an outside source to produce a primary infection, or an endogenous infection may be activated to produce a secondary infection. The latter type of infection occurs more frequently than the former type. For example, Craighead et al. (8) found that 90% of the seropositive recipients became infected, while only 47% of the seronegative became infected. Our own rates, 80% and 59% (see below) are consistent with this experience. Kanich and Craighead (18) pointed out in a retrospective autopsy study that only patients who had received immunosuppressive agents (azathioprine, prednisone, azaserine, and actinomycin C, in various combinations) became infected. Immunosuppressive drugs may contribute to infection by facilitating reactivation or primary infection, but their relative importance in these two types of infections is unknown. In this paper we will review what is known about each risk factor (Table 1), present some data from our laboratory regarding the role of transfused blood, the donated kidney, and the host versus graft reaction (factors A3, A4, and B4), and estimate quantitatively their roles in producing CMV infection. The role of immunosuppressive drugs (factor B2) is treated in greater detail in a separate communication (11).