Epidemiology of herpes simplex

Large differences in HSV-1 seroprevalence are seen in different European countries. HSV-1 seroprevalence is high in Bulgaria (83.9%) and the Czech Republic (80.6%), and lower in Belgium (67.4%), The Netherlands (56.7%), and Finland (52.4%).^[7]

The typical age at which HSV-1 infection is acquired ranges from 5 to 9 years in Central and Eastern European countries like Bulgaria and the Czech Republic, to over 25 years of age in Northern European countries such as Finland, The Netherlands, Germany, and England and Wales. Young adults in Northern European countries are less likely to be infected with HSV-1. European women are more likely to be HSV-1 seropositive than men.^[7]

HSV-2 seropositivity is widely distributed in Europeans older than 12, although there are large differences in the percentage of the population exposed to HSV-2. Bulgaria has a high (23.9%) HSV-2 seroprevalence relative to other European countries: Germany (13.9%), Finland (13.4%), Belgium (11.1%), The Netherlands (8.8%), the Czech Republic (6.0%), and England and Wales (4.2%).^[7]

Women are more likely to be seropositive than men, and likely acquire the virus at an earlier age. In each country of Europe, HSV-2 seropositivity becomes more common from adolescence onwards and increases in the population with age, with a decline in the older age groups in some countries.^[7]

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The most recent data for HSV-2 was published in March 2010, based on a National Health and Nutrition Examination Survey study performed between 2005 and 2013 by CDC. About 1 in 6 Americans (16.2%) aged 14 to 49 is infected with HSV-2. HSV-2 prevalence was nearly twice as high among women (20.9%) than men (11.5%), and was more than three times higher among blacks (39.2%) than non-Hispanic whites (12.3%).^[8]

The most affected group was black women, with a prevalence rate of 48%. Prevalence increased with age and number of partners. Only 18.9% of those infected had previously been aware of their infection.^[8]

2005–2008 HSV-2 study by demographic

Demographic	HSV-2 Seroprevalence	(Females)	(Males)
Gender	16.2%	20.9%	11.5%
Age: 14–19 yrs	1.4%	2.1%	0.8%
Age: 20–29 yrs	10.5%	14.4%	6.6%
Age: 30–39 yrs	19.6%	25.2%	13.9%
Age: 40–49 yrs	26.1%	32.3%	19.6%
Ethnicity: White, non-Hispanic	12.3%	15.9%	8.7%
Ethnicity: Black, non-Hispanic	39.2%	48.0%	29.0%
Ethnicity: Mexican American	10.1%	13.2%	7.5%
1 lifetime sex partner	3.9%	5.4%	1.7%
2–4 lifetime sex partners	14.0%	18.8%	7.3%
5–9 lifetime sex partners	16.3%	21.8%	10.1%
>10 lifetime sex partners	26.7%	37.1%	19.1%

African Americans and immigrants from developing countries typically have an HSV-1 seroprevalance in their adolescent population that is two or three times higher than that of Caucasian Americans.^[9] Many white Americans become sexually active while seronegative for HSV-1. The absence of antibodies from a prior oral HSV-1 infection leaves these individuals susceptible to herpes whitlow, herpes gladiatorum, and HSV-1 genital infection. Primary genital infection brings with it the risk of vertical transmission to the neonate, and is highest if the mother contracts a primary infection during the third trimester of pregnancy. In the U.S. the number of genital infections caused by HSV-1 is now thought to be about 50% of first episodes of genital infection.^[10][11]

In healthy adults, HSV-2 infection occurs more frequently in the United States than in Europe.

Seroprevalence rates in the United States appeared to be increasing, rising from 16.4% in 1976 to 21.8% in 1994.^[12] However, this trend seems to have reversed itself in recent years, dropping to 17.2% in 2004.^[13]

The current prevalence of genital herpes caused by HSV-2 in the U.S. is roughly one in four or five adults, with approximately 50 million people infected with genital herpes and an estimated 0.5 million new genital herpes infections occurring each year.^[9] African Americans appear more susceptible to HSV-2, although the presence of active genital symptoms is more likely in Caucasian Americans. The largest increase in HSV-2 acquisition during the past few years is in white adolescents. People with many lifetime sexual partners and those who are sexually active from a young age are also at higher-risk for the transmission of HSV-2 in the U.S.^{[14][15][16][17]}

Due to the anatomical nature of the vagina women are at higher risk than men for acquiring HSV-2 infection, and the chance of being infected increases with age. This is evident despite women on average having a lower number of sexual partners.^[9] As of 2022, The CDC reports that 48% of African American women and 46% of African American males in the United States are infected with the HSV-2 virus. ^[18][19]

According to a study in Ontario, of people between the ages of 15 and 16, 26.9% of men, 32% of non-pregnant women, and 55% of pregnant women tested positive for HSV-1 antibodies. Between the ages of 40 and 44, 54.7% of men, 88.7% of women, and 69.2% of pregnant women tested positive for HSV-1 antibodies. The overall age-gender standardized seroprevalence for HSV-1 antibodies was 51.1%.^[20] Teenagers are less likely to be seropositive for HSV-2—antibodies against this virus are only found in 0–3.8% of 15- and 16-year-olds. However, 21% of individuals in their early forties have antibodies against HSV-2, reflecting the sexually transmitted nature of this virus. When standardising for age, HSV-2 seroprevalence in Ontario for individuals between the ages of 15 and 44 was 9.1%. Rates for Canadian people infected with HSV-2 is much lower than estimated levels of HSV-2 seroprevalence in people of a similar age range in the United States.^[20]

HSV-2 seroprevalence in pregnant women between the ages of 15 and 44 in British Columbia is similar, with 57% having antibodies for HSV-1 and 13% having antibodies for HSV-2.^[3] In British Columbia in 1999, the seroprevalence of HSV-2 antibody in leftover serum submitted for antenatal testing revealed a prevalence of 17.3%, ranging from 7.1% in women 15–19 years old to 28.2% in those 40–44 years.^[21] • In attendees at an Alberta sexually transmitted infection (STI) clinic in 1994 and 1995, the seroprevalence of HSV-1 and -2 in leftover sera was 56% and 19%, respectively.^[22] In Nova Scotia, 58.1% of 1,790 HSV isolates from genital lesion cultures in women were HSV-1; in men, 36.7% of 468 isolates were HSV-1^[23]

HSV-2 is more common in Sub-Saharan Africa than in Europe or the North America. Up to 82% of women and 53% of men in Sub-Saharan Africa are seropositive for HSV-2. These are the highest levels of HSV-2 infection in the world, although exact levels vary from country to country in this continent.^[24]

In most African countries, HSV-2 prevalence increases with age. However, age-associated decreases in HSV-2 seroprevalence has been observed for women in Uganda and Zambia, and in men in Ethiopia, Benin, and Uganda.^[3]

Genital herpes appears less common in Northern Africa compared to Sub-Saharan Africa. For example, only 26% of middle-aged women have antibodies for HSV-2 in Morocco.^[5] Women are more likely to be infected with HSV-2 once they are over the age of 40.^[5]

Children in Egypt with acute lymphoblastic leukemia are often infected with HSV from a young age—HSV-1 or HSV-2 antibodies are present in an estimated 54% of children under the age of 5, and 77% in children over 10 years of age.^[25] Algerian children are also likely to acquire HSV-1 infection at a young age (under 6) and 81.25% of the population has antibodies to HSV-1 by the age of 15.^[26]

Relative to rates in Europe and North America, HSV-2 seroprevalence is high in Central and South America. Infection levels are estimated at 20% to 60%.^[3][24] During the mid-1980s, HSV-2 prevalence was 33% in 25- to 29-year-old women and 45% in those aged 40 and over in Costa Rica. In the early 1990s HSV-2 prevalence was approximately 45% among women over 60 in Mexico.^[3]

The highest HSV-2 prevalence in Central or South America—60%—has been found in Colombian middle-aged women, although similar HSV-2 prevalence has been observed in younger women in Haiti (54%).^[3] HSV-2 infects about 30% of women over 30 years old in Colombia, Costa Rica, Mexico, and Panama. HSV-2 antibodies were found in more than 41% of women of childbearing age in Brazil.^[3]

However, no increase in seroprevalence was associated with age in women over 40 years old in Brazil—HSV-2 prevalence was estimated at 50% among women aged 40–49, 33% among women 50–59, and 42% among women over 60. Women in Brazil are more likely to acquire an HSV-2 infection if their male partners had history of anal sex and had many sexual partners in his lifetime.^[5] In Peru, HSV-2 prevalence is also high among women in their 30s but is lower in men.^[3]