HSV-1 as a Cause of Genital Herpes: Increasing Incidence
HSV-1 now accounts for a substantial and increasing proportion of genital herpes cases, particularly in young adults, with some populations showing HSV-1 causing 50-70% of new genital herpes infections in individuals under 30 years of age. 1, 2
Epidemiological Trends
The landscape of genital herpes has shifted dramatically over the past two decades:
- In young women ≤30 years old, HSV-1 causes approximately 70% of genital herpes cases, representing a marked departure from historical patterns where HSV-2 predominated 2
- In young men of the same age range, HSV-1 accounts for approximately 45% of genital herpes isolates 2
- The proportion of HSV-1 genital infections declines sharply with age, dropping from 73.7% in women under 31 years to only 4.5% in women over 60 years 2
- Overall population data shows HSV-1 seroprevalence of 47.8% in US adults aged 14-49 years (2015-2016), though this reflects both oral and genital infection 1
Mechanism Behind the Shift
The increasing incidence of HSV-1 genital herpes stems from specific behavioral and immunological factors:
- Changing sexual practices, particularly increased oro-genital contact, directly transmit HSV-1 from oral sites to genital mucosa 3, 4
- Declining childhood HSV-1 acquisition means more young adults remain HSV-1 seronegative and susceptible to genital infection during sexual debut 5
- Condom use during intercourse (but not during oral sex) may paradoxically increase the relative proportion of HSV-1 genital infections by preventing HSV-2 transmission while allowing oral-genital HSV-1 transmission 4
Critical Clinical Distinctions
Understanding the differences between HSV-1 and HSV-2 genital infections is essential for patient counseling:
- Genital HSV-1 recurs significantly less frequently than HSV-2, with a recurrence rate of 1.3 episodes/year in the first year, declining to 0.7 episodes/year in the second year 6
- 43% of patients with primary genital HSV-1 experience no recurrences in the first year, and 67% have no recurrences in the second year 6
- The initial clinical presentation of genital HSV-1 is indistinguishable from HSV-2, making laboratory typing essential for accurate prognosis 3
- Genital HSV-1 has less viral shedding and fewer recurrences compared to HSV-2, particularly after the first year 7
Diagnostic Implications
The rising incidence of HSV-1 genital herpes necessitates specific diagnostic approaches:
- Viral typing should be performed on all genital herpes isolates because the natural history and recurrence patterns differ substantially between HSV-1 and HSV-2 3, 6
- Type-specific serologic testing can distinguish HSV-1 from HSV-2 antibodies and is useful for diagnosing unrecognized infections 3
- Among HSV-1 seropositive individuals without HSV-2,1.8% report diagnosed genital herpes, suggesting increasing genital HSV-1 transmission 5
Common Pitfalls
- Do not assume all genital herpes is HSV-2—this assumption leads to inaccurate prognostic counseling, particularly in young adults 2
- Do not prescribe long-term suppressive therapy for genital HSV-1 without considering the low recurrence rate—suppressive therapy for genital HSV-1 has not been shown to reduce transmission to sexual partners 7
- Do not overlook the psychological impact of misdiagnosis—patients with genital HSV-1 have a significantly better prognosis than those with HSV-2, and accurate typing reduces unnecessary anxiety 6
Public Health Context
- Most genital herpes infections (80-90%) progress subclinically, yet transmission occurs during asymptomatic viral shedding 3
- The stigma associated with HSV-2 is greater than HSV-1 because HSV-2 is almost exclusively sexually transmitted, while HSV-1 can be acquired through non-sexual contact 3
- HSV-2 vaccines may have limited impact on overall genital herpes prevalence given the substantial and growing contribution of HSV-1 to genital disease burden 2