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Herpes simplex viruses (HSV-1 and HSV-2) are enveloped, double-stranded DNA viruses. They are part of the herpes group, which also includes cytomegalovirus, Epstein-Barr virus, varicella zoster virus, and human herpes virus (HHV-6 and HHV-7). HSV infection is among the most prevalent of all viral infections encountered by humans.
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A study from the United States found an overall incidence of 9.6 per 100,000 births in 2006. Separately, a range of 1 per 3000 to 1 per 20,000 is given for an overall incidence in newborn infants for 2012. Seroprevalence of HSV-1 and HSV-2 in pregnant women in the United States is ∼63% and 22%, respectively.
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Two serologic subtypes can be distinguished by antigenic and serologic tests: HSV-1 (usually affects face and skin above the waist) and HSV-2 (genitalia and skin below the waist). Three quarters of neonatal herpes infections are secondary to HSV-2. HSV-1, however, can be the cause of maternal genital herpes infections in 9% of the cases, and its rate appears to be increasing. HSV infection of the neonate can be acquired at 1 of 3 times: intrauterine, intrapartum, or postnatal. Most infections (85%) are acquired in the intrapartum period as ascending infections with ruptured membranes (4–6 hours is considered a critical period for this to occur) or by delivery through an infected cervix or vagina. An additional 10% of infected neonates acquire the virus postnatally (eg, from someone shedding HSV from the mouth who then kisses the infant). The final 5% of neonatal HSV infections occur in utero. The usual portals of entry for the virus are the skin, eyes, mouth, and respiratory tract. Once colonization occurs, the virus may spread by contiguity or via a hematogenous route. The incubation period is from 2–20 days. Three general patterns of neonatal HSV infection are recognized: disease localized to the skin, eyes, and mouth (SEM); central nervous system (CNS) disease (with or without SEM involvement); and disseminated disease (which also may include signs of the first 2 groups). Maternal infection can be classified as either first-episode or recurrent infections. First-episode infections are further classified as either primary or first-episode nonprimary based on type-specific serologic testing. Primary infections are those in which the mother is experiencing a new infection with either HSV-1 or HSV-2 and has not already been infected with the other virus type. First-episode nonprimary infections are those in which the mother has a new infection with one virus type, usually HSV-2, but has antibodies to the other virus type, usually HSV-1. Infants born vaginally to mothers with a true primary infection are at highest risk, with a transmission rate of 50%. Those born to a mother with a first-episode nonprimary infection are at a somewhat lower risk of 30%. The lowest risk (<2%) infants are those who are born to a mother with recurrent infections. Maternal antibody is not always ...