Herpes simplex virus infections occur throughout the world, with humans serving as the only reservoir. The infection is acquired by intimate mucocutaneous contact between a susceptible host and a symptomatic or asymptomatic host shedding virus during primary infection or reactivation. Because the infection results in lifelong latency, the prevalence in any population is cumulative.
Beyond the neonatal period, most primary HSV-1 infections occur in infancy and childhood and are transmitted primarily by contact with infected saliva. Primary HSV-2 infections are acquired after onset of sexual activity and genital herpes infections are among the most common sexually transmitted infections (STIs).
The prevalence of herpes simplex virus infections is influenced by various factors such as socioeconomic status, age, race, and geographic location. One third of children from lower socioeconomic populations have serologic evidence of herpes simplex virus disease by age 5 years compared with 20% of middle-class individuals. Greater person-to-person contact in crowded living conditions is believed to account for the differences in prevalence.
In the United States, HSV-2 seroprevalence increases from about 20-30% in patients aged 15-29 years to 35-60% in patients aged 60 years. This change represents a 30% increase compared with data from 1976-1980. Factors that increase the frequency of HSV-2 infection in older adolescents and adults include gender (more women than men), race (more blacks than whites), marital status (more divorced individuals than single or married individuals), and place of residence (more city residents than suburban residents).
The seroprevalence rate of HSV-2 in pregnant women ranges from 15-30%. Approximately 10% of pregnant women who are HSV-2 seronegative have a sexual partner who is HSV-2 seropositive and are, therefore, at risk of contracting a primary HSV-2 infection during pregnancy. Transmission typically results from contact with an asymptomatic sexual partner with a reported risk of acquisition of approximately 10%. Overall, approximately 2% of women acquire herpes simplex virus during pregnancy.
Herpes simplex virus has worldwide distribution. The prevalence of genital herpes in developing countries is 2-74% and varies among countries. In African countries that are experiencing HIV epidemics, HSV-2 infection is highly prevalent (>70%). Evidence suggests that genital herpes simplex virus infection increases the risk of HIV infection and that persons infected with both viruses are more likely to transmit HIV.