Introduction Herpes simplex virus type 1 (HSV-1) has emerged as the leading cause of first episode genital herpes among adolescents and young adults. The natural history of genital and oral shedding after first episode genital HSV-1 must be described to understand the risk of transmission to sexual partners.
Methods Persons with laboratory documented first clinical episode genital HSV-1 infection obtained daily self-collected genital and oral swabs for two 30 day sessions starting 2 months and 11 months after the first genital HSV-1 outbreak. HSV was detected in swabs using real-time quantitative HSV-1 PCR. Rates of genital and oral shedding were compared during the first and second swabbing sessions using Poisson regression models.
Results Of 52 persons who completed the first swabbing session, 27 (52%) were HSV-1 seronegative (primary infection) at presentation and 25 (48%) were HSV-1 seropositive at initial presentation. Twenty-five persons completed both sessions (11–12 months). Genital HSV-1 shedding was detected in 176 (12.2%) of 1438 swabs from the first shedding session, and declined to 46 (7.1%) of 645 swabs in the second session. The rate of genital lesions was 61 of 1595 (3.8%) days in the first session and 12 of 746 (1.6%) days in the second session. Oral shedding was detected infrequently, with 3.6% of swabs HSV-1 positive in the first session, and 3.3% during the second session. Oral lesions were rare in both sessions.
Conclusions Genital HSV-1 shedding occurs substantially less frequently than genital HSV-2 shedding, and declines in the first year after genital HSV-1 acquisition. These results will inform counselling messages about risk of sexual transmission to persons with first episode genital HSV-1 infection.