Differentiation of primary from nonprimary genital herpes infections by a herpes simplex virus-specific immunoglobulin G avidity assay.

An immunoglobulin G (IgG) antibody avidity assay which uses protein-denaturing agents and a modification of an enzyme-linked immunosorbent assay have been investigated for their usefulness in distinguishing primary genital herpes simplex virus (HSV) infections from nonprimary infections. Forty-nine serum specimens from patients with primary, recurrent, and nonprimary first-episode genital herpes were studied. The clearest separation was obtained with 6 M urea treatment, giving mean avidity indices of 0.398 for sera < or = 100 days after the infection and 0.879 for sera > 100 days after the infection (P < 0.001). No significant difference in avidity indices was observed between the recurrent and nonprimary first-episode infections. Determination of the avidity of HSV-specific IgG will improve the diagnostic potential of HSV serology.