Herpes simplex virus (HSV) type 1 is causing an increasing proportion of anogenital herpes; however, it is unclear which populations are affected. We describe the contribution of HSV-1 to first-episode anogenital herpes and its associations.

For all cases of first-episode anogenital herpes diagnosed at the Sydney Sexual Health Centre from 1992 to 2006, medical record review was used to confirm the type and anatomical site. Age, sex, HIV status and sexual behaviour data were extracted from the clinic database.

Overall, among 1845 confirmed cases of first-episode anogenital herpes the proportion attributable to HSV-1 increased from 29% to 42% (odds ratio (OR) per 3-year band 1.19; 95% CI 1.11 to 1.27). When stratified by gender of sexual partners the proportion of first-episode anogenital herpes due to HSV-1 increased over time, but only achieved significance in heterosexual women (p<0.01). Among men who have sex with men (MSM), HSV-1 only increased for those less than 28 years of age, 17% in 1992–4 to 76% in 2004–6 (OR per 3-year band 1.58; 95% CI 1.14 to 2.19). The proportion attributable to HSV-1 was higher for anal than genital herpes and MSM were much more likely to have anal disease.

The proportion of first-episode anogenital herpes due to HSV-1 significantly increased among younger MSM and heterosexual women over the 15-year period. In some clinical populations, such as young MSM and women or patients with anal disease, HSV-1 may now account for the majority of first-episode anogenital herpes.