BACKGROUND. The clinical and public health importance of recent reports of patients with CD4+ T-lymphocytopenia without human immunodeficiency virus (HIV) infection is unclear. We conducted investigations to determine the demographic, clinical, and immunologic features of patients with idiopathic CD4+ T-lymphocytopenia; whether the syndrome is epidemic or transmissible; and the possible causes. METHODS. We reviewed 230,179 cases in the Centers for Disease Control and Prevention (CDC) AIDS Reporting System and performed interviews, medical-record reviews, and laboratory analyses of blood specimens from adults and adolescents who met the CDC case definition of idiopathic CD4+ T-lymphocytopenia (< 300 CD4+ cells per cubic millimeter or a CD4+ cell count < 20 percent of total T cells on two occasions and no evidence of infection on HIV testing), their sexual contacts, household contacts, and persons who had donated blood to them. RESULTS. We interviewed 31 of the 47 patients identified with idiopathic CD4+ T-lymphocytopenia and 23 of their contacts. There were 29 male and 18 female patients, with a mean age of 43 years (range, 17 to 78); 39 were white, 4 were Asian, 2 were Hispanic, and 2 were black. Eighteen patients (38 percent) had one or more risk factors for HIV infection: seven had hemophilia, six had engaged in homosexual sex, six had received blood transfusions, and two had had heterosexual sex partners who were at risk for HIV infection. The other 29 patients (62 percent) had no identified risk factors for HIV infection. Nineteen persons (40 percent) had AIDS-defining illnesses (18 had opportunistic infections), 25 (53 percent) had conditions that were not AIDS-defining, and 3 (6 percent) were asymptomatic. We tested blood from 28 patients: 8 (29 percent) were found to have CD4+ T-lymphocyte counts of less than 300 cells per cubic millimeter, and 6 had CD8+ T-lymphocytopenia (< 250 cells per cubic millimeter). Ten sex partners, three household contacts, and four children of the patients, as well as six persons who had donated blood to the patients, were immunologically and clinically normal. CONCLUSIONS. This investigation of patients with idiopathic CD4+ T-lymphocytopenia and unexplained opportunistic infections indicates that the disorder is rare and represents various clinical and immunologic states. The investigation of contacts revealed no evidence of a new transmissible agent that causes lymphocytopenia
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