Missed and misdiagnosis of immunodeficiency: Good syndrome presenting as persistent COVID-19 shedding.

A 61-year-old man was referred to the immunology clinic due to prolonged COVID-19 infection and absent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies. His infection, confirmed by polymerase chain reaction (PCR) testing upon returning to Hong Kong from Vancouver, resulted in a 31-day hospitalization due to persistent positive PCR results, despite his remaining asymptomatic. Laboratory tests revealed lymphopenia, low immunoglobulin levels, and unremarkable serum protein electrophoresis, with all viral serologies, including HIV, being negative. Although he received 3 doses of the Pfizer BioNTech vaccine, he showed no detectable SARS-CoV-2 antibodies. Further evaluation indicated almost-absent CD19 cells and low CD4 and CD8 counts, and coupled with his history of thymoma, this led to a diagnosis of Good syndrome. The patient began subcutaneous immunoglobulin replacement therapy and was started on long-term valganciclovir for moderate cytomegalovirus antigenemia.