BACKGROUND
Cytomegalovirus virus (CMV) infection predominantly affects immunocompromised individuals.1 CMV infection can lead to CMV disease and has been associated with non-relapse mortality following allogeneic hematopoietic stem cell transplant.2 CMV disease post allogeneic transplant commonly affects the lungs or gastrointestinal tract.1,2 CMV retinitis remains an uncommon presentation post allogeneic transplant and can be vision-threatening.3-6 Implementation of prophylaxis and preemptive strategies have reduced the incidence of CMV disease to 10% in the first year post allogeneic transplant.2,7Our case demonstrates the occurrence of polymerase chain reaction (PCR) proven mixed viral retinitis (CMV and varicella zoster virus VZV) post allogeneic stem cell transplant despite multiple prophylactic antiviral therapies, and features CMV retinitis in the absence of CMV DNAemia. This case also highlights the emerging challenge of late CMV disease occurring during secondary prophylaxis with Letermovir. To our knowledge this represents the first reported case of polyviral retinitis in this clinical context.