Rising incidence and prevalence of herpes simplex type 2 infection in a cohort of 26 year old New Zealanders

Objectives: To examine changes in the incidence and prevalence of herpes si mplex type 2 (HSV-2) infection in a birth cohort of 26 year old New Zealand ers in whom seroprevalence had been measured at 3.4% at age 21. Methods: Sera from 869 cohort members were tested using an indirect IgG enz yme linked immunoassay specific to the HSV-2 glycoprotein G. Serological re sults were compared with detailed sexual histories. Results: In all, 96 participants (11%) were seropositive for HSV-2, includi ng at least 56 who seroconverted after their 21st birthday. Among those kno wn to be seronegative at age 21, the annual seroconversion rate was 13.5 ca ses per 1000 per year, compared with 8.1 cases per 1000 per sexually active year before age 21. New infections were associated with female sex and an early age of first intercourse. The average rate of partner change was lowe r in the cohort after age 21, and was only modestly increased among those w ho acquired new HSV-2 infections between ages 21 and 26. Conclusions: HSV-2 seroprevalence has risen sharply in this sexually active cohort, despite a reduction in the overall level of partner change. Increa sed rates of HSV-2 acquisition after age 21 may be due to a higher prevalen ce of infection in the pool of potential partners encountered during the th ird decade of life. Factors related to partner choice may have more influen ce on the risk of HSV-2 infection than the number of sexual partners alone.