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 simplex type 2 (HSV-2) infection in a birth cohort of 26 year old New Zealanders in whom seroprevalence had been measured at 3.4% at age 21.

METHODS

Sera from 869 cohort members were tested using an indirect IgG enzyme linked immunoassay specific to the HSV-2 glycoprotein G. Serological results were compared with detailed sexual histories.

RESULTS

In all, 96 participants (11%) were seropositive for HSV-2, including at least 56 who seroconverted after their 21st birthday. Among those known to be seronegative at age 21, the annual seroconversion rate was 13.5 cases 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 lower in the cohort after age 21, and was only modestly increased among those who 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. Increased rates of HSV-2 acquisition after age 21 may be due to a higher prevalence of infection in the pool of potential partners encountered during the third decade of life. Factors related to partner choice may have more influence on the risk of HSV-2 infection than the number of sexual partners alone.