Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) cause lifetime infection that persists in the host, often in latent form.1 Their clinical manifestations are variable and influenced by the portal of viral entry, degree of host immune competence, and the primary or secondary nature of the disease.1,2 Herpes simplex virus type 1 is primarily associated with oral, pharyngeal, facial, ocular, and central nervous system infections and largely transmitted during childhood by oral secretions and nongenital contact.1 Herpes simplex virus type 2 is almost entirely associated with genital herpetic disease and is mostly transmitted sexually by genital secretions.1,2 Most persons with genital herpes do not know they have the disease, and HSV-2 infection and reactivation are typically asymptomatic which aids the virus spread in the population.1,2 In some developed countries, HSV-1 has recently emerged as the predominant causative agents of primary genital lesions.3,4
Herpes simplex virus infections, especially genital herpes, can be associated with physical pain as well as substantial psychological morbidity.1,2 Infection is also a major cause of morbidity and occasional mortality in immunocompromised patients.1 In addition, the virus can be transmitted perinatally from mother to child, which could be fatal.1,3 Other serious complications in adults include blindness, encephalitis, and aseptic meningitis.1 Of major public health importance is the interaction of HSV-2 with other sexually transmitted infections (STIs), particularly the HIV.4 Observational studies suggested that HSV-2 infection is associated with and fuels the HIV epidemic in sub-Saharan Africa and elsewhere. Herpes simplex virus type 2 remains an important sexually transmitted disease (STD) because of its synergy with HIV.5,6
Prevalence of HSV infection overall and age specific varies markedly by country, region within country, and population subgroups.7,8 Prevalence of HSV-1 is high in most geographic areas worldwide, commonly reaching at least 40% by age 15 years, before increasing to 60% to 90% in older adults.8 Herpes simplex virus type 2 infection is also common. It has been estimated that in 2012, approximately 417 million individuals (range, 274–678 million; 11.3%) worldwide aged 15 to 49 years already infected with HSV-2 and that 19.2 million (range, 13.0–28.6 million) became newly infected with HSV-2.9 Infection is generally higher in women than in men, increases with age, and is highest among populations with high-risk sexual behavior.7,8 Prevalence of HSV-2 is higher in developing countries compared with developed countries, although exceptions exist.7,8
Data on STIs in the Kingdom of Saudi Arabia (KSA) is very limited.10 A combination of a conservative culture with stigmatization of people with STIs, leading to underreporting, along with limited surveillance data and difficulties in diagnosis of some STIs, all contribute to this void in information. Here we report the first national seroprevalence survey to determine the prevalence and epidemiology of HSV infection among the adult Saudi population and coinfection with other STIs, namely, HIV and syphilis.
A cross-sectional survey was conducted among adult Saudi nationals attending Ministry of Health primary healthcare centers across the Kingdom. These clinics provide free GP services in all regions in Saudi Arabia and cater for patients from all socioeconomic classes in the Kingdom. The selection of the health primary healthcare centers was random but took into account willingness of staff at each site to participate in a study as well as the PHCs' geographical coverage, the Saudi population of each Heath Region, and the type of population the PHCs serve (urban or rural). According to the most recent census done in 2010, 70% of the KSA Saudi population live in urban areas and 30% live in rural areas.
During a 1-year period (December 2012–December 2013), 5000 participants who met the eligibility criteria were recruited on a consecutive basis as they attend the selected clinics during the period of patients' recruitment from across the 13 administrative regions in KSA (Fig. 1). The number of participants recruited per region was selected based on the proportion of the number of Saudi inhabitants in each region to the total number of Saudi inhabitants in the country. The numbers of participants from each region living in urban or rural areas were selected proportionally to their total number in each region (see Supplementary Table 1, http://links.lww.com/OLQ/A115). As the prevalence of HSV-2 in KSA is unknown, the sample size was calculated based on an estimated prevalence of 8% derived from data from the Middle East and North Africa region11 and the width of the 95% confidence interval [CI] of 1.5%.
A standardized data collection form was used to obtain information regarding the participants' age, sex, geographic location, level of education, working and marital status, and age of marriage.
Samples Collection and Testing
Blood samples (10 mL) were collected from each participant by a phlebotomist at each PHC and sent to the laboratories for testing. Sera were extracted and tested for HSV infection at the Immunology and Serology Laboratory (PCLMA, King Fahad Medical City, Riyadh, KSA) and for HIV and Treponema pallidum antibodies at the Department of Virology of the Ministry of Health's regional laboratory (Riyadh, KSA). Sera were tested for HSV infection using in vitro diagnostics- enzyme-linked immunoassays (ELISA) specific for HSV-1 and HSV-2 antibodies (IgG/IgM) according to the manufacturer's instructions (Vircell Microbiologist, Granada, Spain). As per the manufacturer, the sensitivity and specificity of the IgG ELISA were 99% (HSV-1) and 91% (HSV-2), and 93% (HSV-1) and 100% (HSV-2), respectively. The sensitivity and specificity of the IgM ELISA were 86% (HSV-1) and 83% (HSV-2), and 100% (HSV-1) and 100% (HSV-2), respectively. The negative, positive, and cutoff controls are run with each batch of samples, and any results below index of 9 is considered as negative, index between 9 and 11 is considered equivocal, and index higher than 11 is considered positive. In our clinical Immunology/Serology laboratory at KFMC, we are following College of American Pathologist and Clinical and Laboratory Standards Institute guidelines for method validation of our tests whenever possible (parallel testing, sensitivity and specificity, linearity, precision, and accuracy). In the case of ELISA HSV tests used in this study, our results for sensitivity, specificity, and cutoff come closer to that given by the manufacturer (data not shown). In the cohort of this study, there were clear cut results between positive and negative results for HSV-1 and HSV-2. The few equivocal results were confirmed by Western blot using IVD- and CE-marked HSV-1 and HSV-2 Western blot (anti–HSV-1/HSV-2 gG-2 Euroline-WB IgM/IgG) and performed according to the manufacturer's instructions (Euroimmun, Lubeck, Germany).
Tests for syphilis and HIV infections were performed using the ARCHITECT Syphilis TP12 and the ARCHITECT HIV Ag/Ab Combo13 assays, respectively, using Chemiluminescent Microparticle Immunoassay technology, and according to the manufacturer's instructions (Abbott GmbH & Co KG, Wiesbaden, Germany). All positive HIV samples were confirmed using the commercially available INNO-LIA HIV-1/HIV-2 Ab assay according to the manufacturer's instructions (Innogenetics, Ghent, Belgium).
The study was approved by the King Fahad Medical City Institutional Review Board. All participants were recruited on a voluntary basis and gave written consent before being included in the study. Participants were eligible to be included in the study if they were adult (≥18 years old), Saudi nationals, and willing to participate. Results of the tests were available to all participants. Those who tested positive for HSV-2, T. pallidum antibodies, or HIV infection were notified with the results and advised on the appropriate course of action and have been followed up by their regional Ministry of Health hospitals with free treatments according to international guidelines.
Descriptive statistics were used to present the results (mean, range, percentages). χ2 Tests were performed using OpenEpi (www.openepi.com). P values less than 0.05 were considered statistically significant. A multivariate logistic regression analysis was done for different independent factors using SPSS version 16.
Serology results for HSV infection were available for 4985 participants enrolled from across the 13 administrative regions in Saudi Arabia. Demographics data are summarized in Table 1. The mean age of the participants was 33 years (range, 18–113 years), with a male-to-female ratio of 1.3:1. Most participants (68.4%) lived in urban areas. Information on marriage status was available for 4901 participants, most of whom (73.5%) were or have been previously married (married, divorced, or widowed). The mean marriage age was 23 years. More than half of the participants declared that they were working at the time of the study.
Prevalence of HSV-1 and HSV-2 Infection in Saudi Arabia
The overall prevalence of HSV-1 and HSV-2 in the enrolled population was 88.8% and 1.26%, respectively. Most (84%) of those infected with HSV-2 were also coinfected with HSV-1. For HSV-1, prevalence was statistically significantly higher among females, those living in rural areas, those who were married (married, divorced, or widowed), those with low education, and those working (Table 1). Prevalence also differed depending on age and age of marriage, with prevalence being high among the young (75.8% for those aged 18 years) and increasing with age. Rate of HSV-1 infection was highest (93.1%) among those married at younger age (before 18 years old). Overall prevalence was high (<86%–100%) across most geographical areas (Table 2), with the exception of Al-Qassim region (Fig. 1), where HSV-1 seroprevalence was significantly lower (62.2%). The prevalence of HSV-1 as a function of age for each 5-year age group, along with the 95% CI, is shown in Figure 2. A multivariate logistic regression analysis showed that the odds ratio (OR) for HSV-1 positivity was negatively associated with never having been married (OR, 0.547; 95% CI, 0.424 to −0.707; P < 0.001) and being in a rural area (OR, 0.535; 95% CI, 0.421–0.68; P < 0.001) and positively associated with being older than 30 years (OR, 1.584; 95% CI, 1.236–2.031)
For HSV-2, generally similar patterns to HSV-1 were observed, although the differences between most categories did not reach statistical significance (Table 1). Herpes simplex virus type 2 was more prevalent among females, those living in urban areas, those who were married (married, divorced, or widowed), and those working. Participants with low education had a statistically significantly higher HSV-2 infection rate. Prevalence of HSV-2 is correlating with years of sexual activity. Prevalence of HSV-2 varied across regions (Table 2) and was highest in the Eastern province and Makkah region (2.13% and 1.86%, respectively). Trends for HSV-1 and HSV-2 coinfection were similar to those observed for HSV-2 (Tables 1 and 2).
Recent HSV-1 infection (as evidenced by IgM-positive results) was seen in 85 (1.7%) individuals. Of these cases, 54% were females, 63.5% were from urban areas, and 36% were never married. Only 19.5% of recent HSV-1 infections were among those with low education and 51% and 45% were among those older than 18 to 30 years and those older than 30 to 50 years, respectively. Recent HSV-2 infection was evident in 29 (0.6%) individuals. Of these cases, 45% were females, 48% were from urban areas, and 24% were never married. Approximately 45% of recent HSV-2 infections were among those with higher education and 48% were among those older than 18 to 30 years. Another 48% of the cases were among those older than 30 to 50 years. The prevalence of HSV-2 as a function of age for each 5-year age group, along with the 95% CI, is shown in Figure 3. A multivariate logistic regression analysis did not reveal any significant factors.
HSV and Syphilis Coinfection in Saudi Arabia
Serological results for T. pallidum antibodies were available for 4906 participants from across the Kingdom, of whom 27 (0.55%) were positive (Fig. 1). Of these cases, 15 were males, 19 lived urban areas, and 6 have never been married. There was no statistical difference in prevalence across the geographic regions (P = 0.52), sex (P = 1), location (P = 1), marital status (P = 0.82), or marriage age (P = 0.81). However, participants with low education level had a statistically higher prevalence of T. pallidum seropositivity (1.16%, P = 0.001). Prevalence was also highest among those older than 50 years (3.57%, P < 0.0001). All of the cases with positive T. pallidum antibodies were coinfected with HSV-1, one was coinfected with HSV-2 and another with HIV (Table 3).
HSV and HIV Coinfection in Saudi Arabia
Serology results for HIV infection were available for 4947 participants, 3 (0.06%) of whom were found to be HIV positive. All were males, living in urban areas, and not working at the time of the screening. Two participants (a 22- and a 23-year old) were from the Jizan area and have never been married. The other was a 41-year-old married person living in the Madinah area (Fig. 1). All HIV-positive participants were coinfected with HSV-1, one was positive for T. pallidum antibodies and another was seropositive for HSV-2 (Table 3).
Data on STIs in Saudi Arabia, including the prevalence of HSV infection, are scarce.10,14 We conducted the first national seroprevalence survey of HSV infection in the adult Saudi population.
Herpes simplex virus type 1 was highly prevalent in the population, much more frequent than HSV-2, mostly acquired before adulthood and increased with age. This is in accordance with the known epidemiology of HSV-1 worldwide. Data from across the globe reports that HSV-1 seroprevalance are high in most geographical areas and more prevalent than HSV-2 in all non–high-risk populations surveyed.8 In such population, HSV-1 prevalence increases rapidly with age followed by saturation in adulthood.8 US population–based surveys showed that HSV-1 prevalence consistently increased with age, from 44% in young adults (12–19 years) to 90% among those older than 70 years.15 Few studies investigated HSV-1 prevalence from the Middle East. Data from Syria report HSV-1 prevalence of 55% among children (1–5 years), 80% among young adults (11–20 years), and 94% for those aged over 30 years.8 Studies from the Kingdom found that more than 84% of the pregnant Saudi women surveyed had detectable HSV-1 IgG antibodies and 6–7% had HSV-1 IgM antibodies.16,17 These results are in accordance with ours.
Herpes simplex virus type 2 infection in our study was not apparent in young adults, and the overall prevalence rate (1.26%) was very low compared with rates reported worldwide.7,8 Prevalence of HSV-2 in non–high-risk population varies across the world, with the highest rates reported from sub-Saharan Africa reaching more than 80% in those older than 35 years. Rates between 5% and 60% have been reported from Latin America, 4% to 39% from Europe, 4% to 59% from North America, and 10% to 30% from Asia.8,11 Prevalence of HSV-2 in the general population in the Middle East and North Africa is comparatively low in relation to the rest of the world at 0 to 15%.11 Studies from Syria reported low HSV-2 rates among healthy men and women, with rates of 0.3% to 1.2% and 0%, respectively.8,11 The rate increased to 34% among female sex workers.11 In Turkey, the reported rate of HSV-2 among sexually active adults was 4.8% and increased to 60% among female sex workers.11A study from Iraq found that HSV-2 seroprevalence among 91 pregnant women surveyed was 2.2%.18 Publications from the Kingdom detected HSV-2 IgG antibodies in 6.8% of the pregnant Saudi women surveyed and HSV-2 IgM in 0.5%.16,17 Among women in this study, HSV-2 seroprevalence was only 1.48 (vs. 6.8% in earlier studies. The difference is related to the included populations in these studies. The current study is a community based and included all women, whereas the other studies included pregnant women only. A number of factors could explain the low prevalence of HSV-2 among the general population and especially young adults in the Middle East region including KSA. These factors include the conservative culture of the populations in this region, where multiple partners and extramarital sex are uncommon and where sexual activity commonly starts in adulthood after marriage.10,11,18 In addition, male circumcision is a common practice in the region, where it is the practice that all children undergo circumcision in the early few days of life. This practice has been shown to reduce the risk of HSV-2.19
In our study, HSV-2 prevalence increased with age and was higher among those with low education level. Also, although not reaching statistical significance, prevalence was higher among females, people who were married (married, divorced, or widowed), and among those who married at a younger age. Published data report that old age, female sex, early age at first intercourse, prior STDs, higher number of sexual partners, poor socioeconomic status, and low level education are all risk factors for genital herpes.1 An examination of the Saudi culture could explain our results. Herpes simplex virus type 2 is a lifetime infection and is mainly sexually transmitted. Hence, it is expected that in a society where extramarital sex is uncommon and first intercourse commonly starts after marriage, HSV-2 prevalence increases with age and is more common among those who married at a younger age. Most studies report HSV-2 to be more prevalent among women.7,8 In Western societies, there is a 6-time greater chance of HSV-2 transmission from men to women compared with transmission from women to man.20 Studies from more conservative societies in the Middle East reported mixed results, and some found higher prevalence of HSV-2 in men compared with women.8
We found that rural areas had higher prevalence of HSV-1 than urban regions. This may be due to the fact that rural areas are more tight knit communities where HSV-1 transmission is facilitated, for example, by sharing utensils during food gatherings and community events. This difference was not apparent for HSV-2, where seroprevalence was similar in urban and rural areas. It is reasonable to assume that in urban areas with larger and more mixed populations that are socially more interactive, HSV-2 prevalence would be higher than that in rural areas. However, the conservative culture of the Kingdom may negate this effect. This is supported by the observation that rates of HSV-1 and HSV-2 were lowest in Al-Qassim region, the most conservative region of the Kingdom.
In our study, the prevalence of T. pallidum antibodies and HIV infection among the participants was very low, which is in accordance with published data from the Kingdom.10,21,22 Among Saudi residents, only 1426 cases (1.7 per 100,000 population) were reported from 1995 to 1999).10 In obstetric populations, reported rates of syphilis in the Kingdom ranged between 0 and 0.85%, supporting low prevalence.21 Similarly, although maybe underestimated and on the increase, prevalence of HIV among the Saudi population is low. Between 1984 and 2001, a total of 6046 HIV infections were diagnosed in Saudi Arabia, of which only 1285 (21.3%) cases were Saudi citizens.22
Herpes simplex virus infection is associated with other STDs. Syphilis is synergistically associated with HIV, with syphilis infection enhancing transmission and acquisition of HIV, and HIV suppressing serologic detection of syphilitic infection.23 Herpes simplex virus type 2 is a predictor for incident HPV infection likely because it is also a marker for high-risk sexual activity.24,25 A study of STI clinic attendees in India found that 30% of HSV-2–positive patients had coinfection with HIV-1, 22% had syphilis, and 7.4% had coinfection with both HIV and syphilis.26 One study from a hospital in Saudi Arabia reported that the rate of HIV infection in HSV positive women between 2003 and 2011 was 13.1%.14 This rate is much higher than that in our study. We found that among the HSV-2–positive participants, only 1.6% were coinfected with either HIV or syphilis. However, correlation between HSV-2 infection and HIV was significant.
In the absence of an effective vaccine and a therapeutic cure, monitoring the prevalence of herpes virus in the Saudi population can help inform targeted strategies to prevent new infections, neonatal transmission and complications, and the spread of other STIs. Primary prevention of HSV-2 infection may be an available strategy for reducing the risk of infection by HIV.27 Herpes simplex virus type 2 seroprevalence could potentially be used as a marker for HIV risk within the Kingdom and could offer an effective tool for probing hidden risk behaviors in a region where quality behavioral data are limited.11 The level of HSV-1 among the young should also be monitored as well as the proportion of genital herpes caused by HSV-1. Observations from other countries notice an increase in young people entering adolescence without HSV-1 antibodies.28 The lack of HSV-1 antibodies before sexual debut may render young people susceptible to genital HSV-1 acquisition if exposed and increases the likelihood of developing symptomatic disease if infected with HSV-2.28,29
Our study has some limitations. We chose a sampling methodology that minimizes sampling bias and gives a representative sample of the adult Saudi population. However, we cannot exclude the possibility of some potential biases in the recruitment process. For example, some high-risk individuals could have refused participation in the study. Because of the conservative nature of the Saudi population, information regarding sexual behavior and habits of the participants was not available to support an analytical design for the study; hence for example the prevalence of STIs in high-risk populations was not possible to be determined. Herpes simplex virus infection, especially HSV-2, has been shown to increase significantly among populations with high-risk sexual behavior.8 It is possible that HSV-2 prevalence as well as coinfection with other STIs is higher in such a subpopulation than the overall rates reported in this study. In addition, we used only serology to determine infection and no information on the type of infection and clinical symptoms was available. This meant that the number of symptomatic participants, those with genital lesions, and the proportion of HSV-1 responsible for genital herpes in our study could not be determined.
Nevertheless, we report the first national study on seroprevalence of HSV infection in the adult Saudi population. We found that HSV-1 infection is highly prevalent and mostly acquired before adulthood. Contrary to HSV-1, HSV-2 prevalence was low, was acquired in adulthood, was correlating with start of sexual activity, and increased with age. Prevalence of T. pallidum antibodies and HIV in the sampled population was very low, as was the prevalence among HSV-2–positive participants. Further work is warranted to monitoring the prevalence of HSV in the Saudi population, including subpopulation groups such as pregnant women and high-risk populations, as well as the proportion of genital herpes caused by HSV-1 to detect any changes in the epidemiology of the virus. In addition, we did not perform confirmatory testing for T. pallidum infection and we did not know clinical signs and symptoms. And because treponemal assays will be positive even after active syphilis infections have been treated, the attempts to calculate prevalence of syphilis in Saudi Arabia could not be accurately determined.
1. Fatahzadeh M, Schwartz RA. Human herpes simplex virus infections: epidemiology, pathogenesis, symptomatology, diagnosis, and management. J Am Acad Dermatol 2007; 57: 737–763.
2. Azwa A, Barton SE. Aspects of herpes simplex virus: A clinical review. J Fam Plann Reprod Health Care 2009; 35: 237–242.
3. Anzivino E, Fioriti D, Mischitelli M, et al. Herpes simplex virus infection in pregnancy and in neonate: Status of art of epidemiology, diagnosis, therapy and prevention. Virol J 2009; 6: 40.
4. Chentoufi AA, Dervillez X, Rubbo PA, et al. Current trends in negative immuno-synergy between two sexually transmitted infectious viruses: HIV-1 and HSV-1/2. Curr Trends Immunol 2012; 13: 51–68.
5. Freeman EE, Weiss HA, Glynn JR, et al. Herpes simplex virus 2 infection increases HIV acquisition in men and women: Systematic review and meta-analysis of longitudinal studies. AIDS 2006; 20: 73–83.
6. Wald A, Link K. Risk of human immunodeficiency virus infection in herpes simplex virus type 2–seropositive persons: A meta-analysis. J Infect Dis 2002; 185: 45–52.
7. Looker KJ, Garnett GP, Schmid GP. An estimate of the global prevalence and incidence of herpes simplex virus type 2 infection. Bull World Health Organ 2008; 86: 805–812.
8. Smith JS, Robinson NJ. Age-specific prevalence of infection with herpes simplex virus types 2 and 1: A global review. J Infect Dis 2002; 186 (suppl 1): S3–S28.
9. Looker KJ, Magaret AS, Turner KM, et al. Global estimates of prevalent and incident herpes simplex virus type 2 infections in 2012. PLoS One 2015; 10: e114989.
10. Madani TA. Sexually transmitted infections in Saudi Arabia. BMC Infect Dis 2006; 6: 3.
11. Abu-Raddad LJ, Schiffer JT, Ashley R, et al. HSV-2 serology can be predictive of HIV epidemic potential and hidden sexual risk behavior in the Middle East and North Africa. Epidemics 2010; 2: 173–182.
12. Wellinghausen N, Dietenberger H. Evaluation of two automated chemiluminescence immunoassays, the LIAISON Treponema Screen and the ARCHITECT Syphilis TP, and the Treponema pallidum
particle agglutination test for laboratory diagnosis of syphilis. Clin Chem Lab Med 2011; 49: 1375–1377.
13. Chavez P, Wesolowski L, Patel P, et al. Evaluation of the performance of the Abbott ARCHITECT HIV Ag/Ab Combo Assay. J Clin Virol 2011; 52 (suppl 1): S51–S55.
14. Fageeh WM. Sexually transmitted infections among patients with herpes simplex virus at King Abdulaziz University Hospital. BMC Res Notes 2013; 6: 301.
15. Xu F, Sternberg MR, Kottiri BJ, et al. Trends in herpes simplex virus type 1 and type 2 seroprevalence in the United States. JAMA 2006; 296: 964–973.
16. Obeid OE. Prevalence of herpes simplex virus types 1 and 2 and associated sociodemographic variables in pregnant women attending King Fahd Hospital of the university. J Family Community Med 2007; 14: 3–7.
17. Alzahrani AJ, Obeid OE, Almulhim AA. Analysis of herpes simplex 1 and 2 IgG and IgM antibodies in pregnant women and their neonates. Saudi J Obstet Gynaecol 2005; 5: 53.
18. Hasan ASH, Al-Duliami AA, Hwaid AH, et al. Seroprevalence of anti–herpes simplex virus type 2 IgG, IgM antibodies among pregrant women in Diyala province. Diyala J Med 2013; 5: 36–43.
19. Mugo N, Dadabhai SS, Bunnell R, et al. Prevalence of herpes simplex virus type 2 infection, human immunodeficiency virus/herpes simplex virus type 2 coinfection, and associated risk factors in a national, population-based survey in Kenya. Sex Transm Dis 2011; 38: 1059–1066.
20. Garnett GP, Dubin G, Slaoui M, et al. The potential epidemiological impact of a genital herpes vaccine for women. Sex Transm Infect 2004; 80: 24–29.
21. Al-Sibiani SA. Prenatal screening syphilis: Is universal screening necessary in Saudi Arabia. JKAU: Med Sci 2008; 15: 41–48.
22. Madani TA, Al-Mazrou YY, Al-Jeffri MH, et al. Epidemiology of the human immunodeficiency virus in Saudi Arabia; 18-year surveillance results and prevention from an Islamic perspective. BMC Infect Dis 2004; 4: 25.
23. Tobian AA, Quinn TC. Herpes simplex virus type 2 and syphilis infections with HIV: An evolving synergy in transmission and prevention. Curr Opin HIV AIDS 2009; 4: 294–299.
24. Caldeira TD, Goncalves CV, Oliveira GR, et al. Prevalence of herpes simplex virus type 2 and risk factors associated with this infection in women in southern Brazil. Rev Inst Med Trop Sao Paulo 2013; 55: 315–321.
25. Fukuchi E, Sawaya GF, Chirenje M, et al. Cervical human papillomavirus incidence and persistence in a cohort of HIV-negative women in Zimbabwe. Sex Transm Dis 2009; 36: 305–311.
26. Chopra S, Devi P, Devi B. Herpes simplex virus 2: A boon to develop other sexually transmitted infections. J Indian Med Assoc 2013; 111: 236–238.
27. Centers for Disease Control and Prevention (CDC). Seroprevalence of herpes simplex virus type 2 among persons aged 14–49 years—United States, 2005–2008. MMWR Morb Mortal Wkly Rep 2010; 59: 456–459.
28. Bradley H, Markowitz LE, Gibson T, et al. Seroprevalence of herpes simplex virus types 1 and 2—United States, 1999–2010. J Infect Dis 2014; 209: 325–333.
29. Langenberg AG, Corey L, Ashley RL, et al. A prospective study of new infections with herpes simplex virus type 1 and type 2. Chiron HSV Vaccine Study Group. N Engl J Med 1999; 341: 1432–1438.