Herpes simplex virus type 1 (HSV-1) serostatus is measured from serum samples using solid-phase enzyme immunoassay at Stanley Laboratory of Developmental Neurovirology at the Johns Hopkins School of Medicine, blinded to participants’ clinical characteristics. Assays are performed using a purified viral envelope glycoprotein gG-1 as the solid-phase antigen. Reagents for HSV-1 assays are obtained from Focus Diagnostics. Specimens are classified as seronegative if the immune status ratio, determined by comparison with defined standards, is less than 1.0, or as seropositive if the ratio is ≥1.0.