In the past decade, investigations have amply documented the increase in the frequency of genital herpes simplex virus type 1 (HSV-1) compared with genital HSV-2 infection. This trend has been seen both in Europe and in the United States, and it is comprehensively documented in New South Wales, Australia, on p 255 of this issue of STI.¹ The issues raised by this observation have implications for understanding changes in HSV seroprevalence and sexual behaviour over time, and for patient management and counselling.

What accounts for the rise in the frequency of genital HSV-1? First of all, it needs to be acknowledged that genital HSV-1 infection has been common for a long time. For example, a Japanese study of women, published in 1976, documented 43% of genital herpes as caused by HSV-1.² In 1977, a university health clinic study showed that 37% of women with clinical diagnosis of genital herpes had HSV-1 isolated.³ Among people with newly acquired genital herpes in Seattle in the mid to late 1980s, 32% had genital HSV-1 infection.⁴ Still, several well done studies have shown that the relative proportion of genital HSV-1 isolates has increased even more strikingly in the past two decades.^5–7 Two potential explanations that have been put forth include a decrease in HSV-1 acquisition among children, leaving them susceptible to HSV-1 in adolescence, and increase in oral-genital contact, or initiation of oral sex instead of genital-genital sex, among adolescents. …