Evaluation of the specificity of an immunoprecipitin test for non-A, non-B hepatitis.

The specificity of a new antigen-antibody system (devised at the International Center for Medical Research and Training [ICMRT], San José, Costa Rica) for non-A, non-B (NANB) hepatitis was evaluated. ICMRT antigen was found in eight (21%) of 38 patients with acute NANB hepatitis; 22 patients (58%) seroconverted, including three who were positive for ICMRT antigen. Five patients with chronic NANB hepatitis were persistently positive for ICMRT antigen and negative for ICMRT antibody during several years of observation. Neither ICMRT antigen nor seroconversion was found among 11 patients with hepatitis A and 19 with hepatitis B occurring concomitantly with NANB hepatitis; only two of 56 patients with other liver diseases had ICMRT antigen, both presumably with chronic antigenemia. Seven of 128 household contacts of patients with NANB hepatitis had ICMRT antigen; 27 had antibody initially, and 35 (37% of susceptible contacts) seroconverted during the observation period. Less than 4% of household contacts of patients with hepatitis A or B seroconverted.