Causes of immunosuppression included HIV infection with CD4+ cell count less than or equal to 200/μL (n = 6), HIV infection with CD4+ cell count greater than 200/μL (n = 10), administration of prednisone or equivalent 20 mg/d or greater (n = 5), organ transplant (n = 27), neutropenia (n = 4), chemotherapy (n = 7), splenectomy (n = 2), azathioprine use (n = 2), or methotrexate use (n = 4). Here, CD4 is linked to HIV infectious disease.