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INTRODUCTION

Herpes simplex virus (HSV) is one of the most common infections encountered by humans worldwide. As a member of the herpesvirus family (Herpesviridae), it shares the unique biologic characteristic of being able to exist in a latent state and recur periodically, if not chronically, serving as a reservoir for transmission from one person to another. There are two distinct antigenic types of HSV; HSV-1 and HSV-2. HSV-1 is usually associated with infections above the belt, namely involving the oropharynx and lips; however, a large and increasing number of genital infections in the United States is attributed to HSV-1. HSV-2 routinely causes infections below the belt, involving the genitalia, buttocks, and infrequently the lower extremities. In addition, both viruses can cause infection of the newborn. The spectrum of disease caused by HSV ranges from benign and nuisance infections to those that can be life threatening.1

EPIDEMIOLOGY

HSV infection is transmitted by direct contact with an infected person’s lesions, mucosal surfaces, or genital or oral secretions.2 The epidemiology of infection is best defined by seroprevalence of HSV-1 and HSV-2. HSV infections remain common despite a recent steady decrease in prevalence, as shown in Fig. 123-1.3 The seroprevalence of HSV-1 and HSV-2 increases linearly with age and is higher in females. Primary HSV-1 infections usually occur in the young child and are most often asymptomatic. During the period of 1999–2002, HSV-1 seroprevalence in U.S.-born children ages 6–13 years was 31%, progressively increasing with age.4 In the most recent National Health and Nutrition Examination Survey (NHANES) of 2015–16, the seroprevalence in people age 14–19 years was 27%, consistent with overall trends of decreasing prevalence of HSV-1 in early childhood over the last two decades.2 By adulthood, about half of the U.S. population (48%) has experienced HSV-1 infection.2 HSV-1 prevalence differs by race and ethnicity, with prevalence highest in the Mexican American population and lowest in non-Hispanic whites, a finding that remains true despite a steady decline in overall prevalence in the United States. The HSV-1 contribution to genital herpetic disease has increased over the past two decades. The percentage of people who randomly tested positive for HSV-1 only and had a diagnosis of genital herpes increased to 1.8% in NHANES survey 1999–2004 when compared to 0.4% in the NHANES survey 1988–94.5 A retrospective evaluation of college students with newly diagnosed genital infection from 1993 to 2001 showed a striking increase of HSV-1 as a cause of symptomatic genital herpes from 30.9% in 1993 to 77.6% in 2001.6

FIGURE 123-1

Downward trends of HSV-1 (A) and HSV-2 (B) age-adjusted prevalence in the U.S. population 14–49 years based on the National Health and Nutrition Examination Survey, 1999–2016. 1 significant linear trend with p < 0.05. (Source: McQuillan G, Kruszon-Moran D, Flagg EW, Paulose-Ram R. Prevalence of herpes simplex virus type 1 and type 2 in persons ...

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