- Immunodeficiency [e.g., absolute neutrophil count <500/mm^3, chronic immunosuppressive drugs, active chemotherapy, or known acquired immunodeficiency syndrome (AIDS) (CD4 count <200 or AIDS-defining illness within the last year) assessed by patient history]. Note: patients who had prior AIDS-defining illness or CD4 count <200 in the past may be enrolled if most recent CD4 count >200;