Background: Genital herpes simplex virus type 1 (HSV-1) has emerged as the leading cause of first-episode genital herpes among specific populations in the United States, such as adolescents, young adult women, and men who have sex with men (MSM). We examined trends in the etiology of first-episode genital herpes diagnoses over time in a sexually transmitted disease (STD) clinic population.
Methods: Using an electronic database, we identified persons diagnosed as having first-episode genital herpes at Public Health - Seattle & King County STD Clinic from 1993 to 2014 and compared risk factors for genital HSV-1 versus herpes simplex virus type 2 (HSV-2) infection.
Results: Of 52,030 patients with genital ulcers, 3065 (6.15%) had first-episode genital herpes infection: 1022 (33.3%) with HSV-1 and 2043 (67.7%) with HSV-2. Overall, 1154 (37.7%) were women, the median age was 28 years (interquartile range, 24-36 years), 1875 (61.2%) patients were white, and 353 (11.5%) were MSM. The number of patients diagnosed as having first-episode genital HSV-2 declined on average by 5.5 persons per year, from 208 in 1993 to 35 in 2014 (change of -5.6 per year; 95% confidence interval [CI], -6.9 to -4.1), whereas HSV-1 diagnoses remained stable at approximately 50 per year (change of 0.2; 95% CI, -0.4 to 0.9). In a multivariate model, persons diagnosed as having first-episode genital HSV-1 rather than genital HSV-2 infection were more likely to be younger (age <30 years [relative risk {RR}, 1.38; 95% CI, 1.22-1.55]), white (RR, 3.16; 95% CI, 2.57-3.88), and MSM (RR, 1.50; 95% CI, 1.31-1.71).
Conclusions: We observed a significant decrease in the frequency of first-episode genital HSV-2 and a stable number of first-episode genital HSV-1 infections in a STD clinic over the last 2 decades.