Is herpes simplex virus type 1 (HSV-1) now more common than HSV-2 in first episodes of genital herpes?

In this issue, Roberts et al. report that while HSV-2 was isolated more frequently from genital cultures at a Midwestern university from 1993 to 1997. HSV-1 became the predominant isolate type from 1997 to 2001.(1) Also in this issue. Samra et al. report that while HSV-2 was the predominate cause of genital herpes in Israel in the 1970s, HSV-1 was the principal cause of genital herpes among persons seeking care at a Tel Aviv medical center from 1993 to 2001.(2) Similarly, a Norwegian study found that 35% of initial first-episode genital herpes cases in 1987 to 1989 were attributable to HSV-1, compared to 66% in 1992 to 1995 and 51% in 1996 to 1998.(3) The changing epidemiology seems to be primarily affecting adolescents and young adults. 1-3 Roberts reports that HSV-1 was significantly more common in persons age 16 to 21 than in those greater than or equal to22 (64% versus 36%, P < 0.001). Among Norwegian patients, a significant increase in the proportion of HSV-1 isolates was noted in persons <21 with initial genital herpes between 1987 to 1989 (41%) and 1992 to 1995 (91%, P < 0.001) and 1996 to 1998 (70% P < 0.001). There was not a similar significant change for persons 21 to 30. and the proportion of HSV-1 isolates for persons >30 years remained at or below 30%. Is HSV-1 now the predominant cause of first episode genital herpes for young persons? The short answer is that we do not know, but these studies certainly argue that HSV-1 is increasing and may be the major cause of new genital infections in certain populations. The two studies reported in this issue are not population-based and we have little demographic information on the participants. It would have been helpful to have information on the number of sexual partners, sexual practices, sexual orientation, socioeconomic status and race/ethnicity of the participants. However, population-based serostudies do not identify the site of infection. and studies that determine the HSV type isolated from first episodes of genital herpes will always be restricted to convenience samples that are not truly population-based.