Most cases of infection with either HSV-1 or HSV-2 do not result in serious morbidity. Morbidity and mortality associated with herpes simplex virus are discussed in Complications. Mortality associated with herpes simplex virus is primarily related to perinatal infection, encephalitis, and infection in individuals who are immunocompromised.
At the time of vaginal delivery, the risk of herpes simplex virus transmission from a mother with true primary herpes simplex virus infection to her infant is approximately 50%. Women with primary infections at delivery are 10-30 times more likely than women with a recurrent infection to transmit the virus to their babies. Infants born to mothers with newly acquired infections who do not have primary infections in the presence of preexisting immunity caused by another viral infection (ie, first-episode nonprimary) have a transmission risk of 25-30%.
The neonatal herpes simplex virus infection rate is considered to be less than 2% when the mother has active infection caused by the shedding of herpes simplex virus acquired before pregnancy or during gestation before the onset of labor (recurrent infection). Approximately two thirds of women who acquire genital herpes during pregnancy have no symptoms. Of mothers who deliver an infant with herpes simplex virus infection, 60-80% have no evidence of genital herpes simplex virus infection at the time of delivery and have no history of previous genital infection and have sexual partners with no history. Of babies born to mothers with a primary infection near the time of delivery, 30-50% acquire the infection.
Currently, neonatal herpes simplex virus disease is estimated to occur in approximately 1 per 3000 deliveries in the United States. A recent study determined that herpes simplex virus infection in neonates and infants was associated with substantial morbidity, mortality, and resource use.
Race
Although the risk of herpes simplex virus infection is not related to race, infection rates in the United States vary with race because of various factors, such as racial and ethnic differences in the prevalence of poverty and low socioeconomic status, access to health care, sexual and health-related behavior, and illicit drug use.
By age 5 years, more than 35% of black children are infected with HSV-1 compared with 18% of white children. Through adolescence, the prevalence of antibodies to HSV-1 in blacks is approximately twice the rate among whites. By age 40 years, HSV-1 seroprevalence is similar among blacks and whites. The prevalence of HSV-2 antibodies among blacks is 3-4 times higher than that among whites.
Seroprevalence among women of childbearing age in the late 1970s was estimated to be 50% for blacks and 20% for whites. By the late 1980s, rates of infection had increased to approximately 60% for blacks and 35% for whites. As shown in 2 nationwide surveys of HSV-2 seroprevalence in the last 2 decades, the cumulative lifetime incidence of HSV-2 reaches 25% in white women, 20% in white men, 80% in black women, and 60% in black men.23 Studies have indicated that the seroprevalence of HSV-2 among Hispanics ranges from 17-22.3%. Infants born to non-Hispanic white women may be at higher risk of herpes simplex virus infections. This is a result of a greater likelihood that these women are herpes simplex virus seronegative and at risk of acquiring a primary HSV-1 or HSV-2 infection in late pregnancy.
Sex
Infection rates with HSV-1 tend to be similar in both genders during early childhood. However, through adolescence, the prevalence of antibodies to HSV-1 is slightly higher among females than among males. Rates of HSV-2 infection are higher in women than in men.24 Nationwide surveys of HSV-2 seroprevalence over the last 2 decades have demonstrated cumulative lifetime incidences of 25% in white women and 80% in black women. This compares with rates of 20% in white men and 60% in black men.
Age
Beyond the neonatal period, most childhood herpes simplex virus infections are caused by HSV-1. The seroprevalence of HSV-1 antibodies increases with age, and its rate is 20% by age 5 years. No increase occurs until 20-40 years of age, when 40-60% of individuals are HSV-1 seropositive. As a reflection of the association between infection and sexual activity, many HSV-2 infections occur around puberty and early adolescence. A progressive increase in HSV-2 infections occurs in all populations beginning in adolescence.24 In the United States, HSV-2 seroprevalence increases from approximately 20-30% in those aged 15-29 years to 35-60% in those aged 60 years. Most neonatal infections are caused by HSV-2, but increasing proportions are being caused by HSV-1.2,