Clinical correlates of index values in the focus HerpeSelect ELISA for antibodies to herpes simplex virus type 2 (HSV-2)

BackgroundClinical correlates of HerpeSelect ELISA index values are poorly understood.ObjectivesThis study was designed to determine the effects of time of infection, test variability, and antibody avidity on index values.Study designSera (N = 313) from 81 patients with new HSV-2 infections and 236 sera from 32 patients with long-standing (median 11.3 years) HSV-2 were tested by HerpeSelect HSV-2 ELISA. High positive, low positive and negative controls were run on 42 test plates to establish test variability.ResultsIndex values tended to rise after infection, peaking a median of 9–10 weeks post-infection (range 8–323 days). Of 32 patients with established HSV-2 infections, 7 (22%) had at least one low index value (>1.1 to ≤3.5), and one had a transient seroreversion event. Test variability of index values was substantially lower than inter- or intra-patient variability. Median antibody avidity was higher in sera with high versus low index values in established infections, but unrelated to index value in patients with early infections.ConclusionsIndex values or index value changes are not absolute indicators of early versus established HSV-2 infection or solely a function of test variability. Low antibody avidity may contribute to low index values once infection is established.