Risk Factors

Risk Factors

Everyone is at risk for herpes simplex virus. According to the latest U.S. data from 1999 - 2004, 57.7% of Americans ages 14 – 49 years are infected with the HSV-1 virus, the main cause of oral herpes and some cases of genital herpes. About 17% of Americans in the same age range test positive for the HSV-2 virus, the main cause of genital herpes. Infection rates for both viruses have declined since the late 1980s. However, infection is lifelong, so once a person is infected, he or she remains infected.

Individuals at Risk for Oral Herpes

Oral herpes is usually caused by HSV-1, which is easily transmitted and is the most common form of the herpes simplex virus. Most people with HSV-1 infection were first infected during childhood, with the highest incidence of first infection occurring between 6 months and 3 years of age. The incidence in children varies among regions and countries, with the highest rates occurring in crowded and unsanitary regions. Studies suggest that by age 5 more than a third of children in low-income areas are infected compared to 20% of children in middle-income areas. However, by the time this more privileged group reaches their thirties, about 60% have become infected with HSV-1. After age 40, socioeconomic differences in infection rates become even less pronounced.

Individuals at Risk for Genital Herpes

The number of Americans with genital herpes increased by 30% from the late 1970s through the early 1990s. However, recent surveys indicate that prevalence is decreasing. A 2006 study in the Journal of the American Medical Association found that among Americans ages 14 - 49 years, the prevalence of HSV-2 (the main cause of genital herpes) decreased by 19% from 1988 - 2004. The decrease was greatest among adolescents between the ages of 14 - 19.

The prevalence of HSV-1 (the main cause of oral herpes) also declined, but the percentage of genital herpes infections caused by HSV-1 more than tripled. Among people infected with HSV-1, but not HSV-2, 1.8% were diagnosed with genital herpes in 1999 -- 2004 compared with 0.4% in 1988 -- 1994. (HSV-2 still causes the majority of genital herpes infections.)