Background: Genital HSV-1 has emerged as the most common cause of first episode genital herpes in the last few decades. We examined trends in etiology of first episode genital HSV infection in a 21-year period and determined risk factors for genital HSV-1 infection.
Methods: Using an electronic database, we identified persons who visited Public Health – Seattle & King County STD Clinic from 1993 through 2014 with genital ulcers. We selected persons who reported a first episode genital ulcers with a positive genital HSV culture. Poisson regression was used to determine risk factors for first episode genital HSV-1 versus HSV-2 infection.
Results: Of 52,030 patients with genital ulcers, 3,199 patients had culture-proven first episode genital HSV infection: 1,059 (33%) with HSV-1 and 2,140 (67%) with HSV-2. Overall, 1213 (37.9%) of patients with first episode genital HSV were female. The median age was 27 (range 13-81). 1959 (61.2%) of the patients were white, and 1344 (42%) were men who have sex with men. Over time, the number of cases of HSV-2 has declined 6% per year, from 223 cases in 1993 to 39 cases in 2014 (RR=0.94, 95% CI=0.93-0.95) while the number of cases of HSV-1 remained stable at ~50/year (RR=1.0; 95% CI: 0.99-1.01). Among patients with first-episode genital HSV, age <30 years (RR=1.39; 95% CI: 1.19-1.62), white race (RR=3.06; 95% CI: 2.4-3.91), and reporting same-sex partners (RR=1.63; 95% CI: 1.11-2.41) were associated with genital HSV-1 infection. Men were less likely to be infected with HSV-1 than women (RR=0.64; 95% CI: 0.51-0.8).
Conclusions: There has been a significant decrease in first episode genital HSV-2 over the last twenty years, with a stable number in cases of first episode genital HSV-1, resulting in an increased proportion of cases attributed to HSV-1. Understanding changing epidemiology in genital HSV infection may inform prevention strategies.