Relationship Between HSV-1 Serostatus and HSV-2 IgG Confirmation Results Using an Inhibition Assay

Approximately 2% of HerpeSelect herpes simples virus type 2 (HSV-2) IgG enzyme immunoassay (screen assay) sera-positive samples do not confirm using an HSV-2 IgG inhibition assay. Of these, roughly 1.33% are confirmed negative, and a small proportion (0.2%) are indeterminate due to inhibition observed with HSV-1 and HSV-2 lysate. The objective of this study was to assess the relationship between HSV-1 IgG serostatus and HSV-2 IgG confirmation results using the HSV-2 IgG inhibition assay.

This study included consecutive HSV-2 IgG screen-positive specimens regardless of index value. Specimens were also tested for HSV-1 IgG. The HSV-2 IgG confirmation results from the inhibition assay were evaluated to assess the relationship between inhibition results and HSV-1 serostatus.

Of the 21,006 positive HSV-2 IgG specimens, 13,237 (63%) were also positive for HSV-1 IgG. The proportion of HSV-1 IgG-positive samples among inhibition-indeterminate samples (33 to 40 [83%]) was higher than among inhibition-negative (167 of 279 [60%]) and inhibition-positive (13,041 of 20,691 [63%]) samples. Among HSV-1 IgG-positive samples, the median HSV-1 IgG index was also significantly higher for the inhibition-indeterminate group (median, 48.8) than for the inhibition-negative (median, 30.7) and inhibition-positive groups (median, 31.2; P = 0.00013 and P = 3.1e - 05, respectively).

These findings suggest that HSV-2 IgG inhibition-indeterminate, but not inhibition-negative, results are associated with higher index values of HSV-1 IgG. Further studies are needed to understand other factors associated with inhibition-indeterminate results.