Update: serologic testing for human T-lymphotropic virus type I--United States, 1989 and 1990.

Human T-lymphotropic virus type I (HTLV-I)* is a retrovirus that has been identified as a cause of human T-cell leukemia/lymphoma and tropical spastic paraparesis; HTLV-II is closely related to HTLV-I but has not been linked to human illness. Both viruses can be transmitted through blood transfusion and injecting-drug use; therefore, accurate and reliable HTLV-I-antibody test results are essential to diagnose HTLV-I infection, conduct public health surveillance and prevention programs, and improve the safety of blood and blood products collected for transfusion (1). During 1989, CDC expanded its Model Performance Evaluation Program (MPEP) to assess the performance of laboratories that conduct HTLV-I-antibody testing and to identify potential problems in the testing process (2). This report summarizes findings of CDC's laboratory performance evaluation surveys.