Comparative clinical manifestations and immune effects of cytomegalovirus infections following distinct types of immunosuppression

Background: Cytomegalovirus (CMV) infection is a well-recognised complication of solid organ and hematopoietic cell transplantation. However, CMV infection also occurs in patients with human immunodeficiency virus infection, previously immunocompetent intensive care unit patients, and individuals on immunosuppressive medications for various underlying diseases. Objectives: This review describes the comparative effects of CMV infection in distinct types of acquired immunosuppression. Sources: Selected peer-reviewed publications on CMV infections published until December 2021. Content: CMV infection affects various organ systems through direct cytolytic mechanisms but may also exert indirect effects by promoting pro-inflammatory and immunosuppressive responses. This has been well studied in transplant recipients, for whom antiviral prophylaxis and pre-emptive therapy have now become standard practice. These strategies not only prevent direct CMV disease manifestations but also mitigate various immunopathological processes to reduce graft-vs.-host disease, graft rejection, and the occurrence of secondary bacterial and fungal infections. The efficacy of neither prophylactic nor pre-emptive treatment of CMV infection has been demonstrated for patients with critical illness- or medication-induced immunosuppression. Many observational studies have shown an independent association between CMV reactivation and a prolonged duration of mechanical ventilation or increased mortality in the intensive care unit. Furthermore, data suggest that CMV reactivation may increase pulmonary inflammation and prolong the duration of mechanical ventilation. Implications: A large number of observational and experimental studies suggest attributable morbidity and mortality related to CMV infection, not only in transplant recipients and patients with human immunodeficiency virus infection but also in patients with critically illness- or medication-induced immunosuppression. Adequately powered randomised controlled trials investigating the efficacy of prophylaxis or pre-emptive treatment of CMV infection in these patients are lacking, with a notable exception for transplant recipients.