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Address correspondence to: Audrey E. Pettifor, Ph.D., M.P.H., Department of Epidemiology, University of North Carolina, CB #7435, McGavran-Greenberg Bldg., Chapel Hill, NC 27599-7435
Department of Epidemiology, University of North Carolina, Chapel Hill, North CarolinaReproductive Health and HIV Research Unit, University of the Witwatersrand, Johannesburg, South Africa
Department of Epidemiology, University of North Carolina, Chapel Hill, North CarolinaDivision of Infectious Diseases, School of Medicine, University of North Carolina, Chapel Hill, North Carolina
Division of General Pediatrics and Adolescent Medicine, Department of Pediatrics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina
Department of Epidemiology, University of North Carolina, Chapel Hill, North CarolinaDivision of Infectious Diseases, School of Medicine, University of North Carolina, Chapel Hill, North Carolina
To compare the sexual behaviors of young people in South Africa (SA) and the United States (US) with the aim to better understand the potential role of sexual behavior in HIV transmission in these two countries that have strikingly different HIV epidemics.
Methods
Nationally representative, population-based surveys of young people aged 18–24 years from SA (n = 7,548) and the US (n = 13,451) were used for the present study.
Results
The prevalence of HIV was 10.2% in SA and <1% in the US. Young women and men in the US reported an earlier age of first sex than those in SA (mean age of coital debut for women: US [16.5], SA [17.4]; for men: US [16.4], SA [16.7]). The median number of lifetime partners is higher in the US than in SA: women: US (4), SA (2); men: US (4), SA (3). The use of condom at last sex is reported to be lower in the US than in SA: women: US (36.1%), SA (45.4%); men: US (48%), SA (58%). On average, young women in SA report greater age differences with their sex partners than young women in the US.
Conclusion
Young people in the US report riskier sexual behaviors than young people in SA, despite the much higher prevalence of HIV infection in SA. Factors above and beyond sexual behavior likely play a key role in the ongoing transmission of HIV in South African youth, and thus should be urgently uncovered to develop maximally effective prevention strategies.
South Africa (SA) is one of the countries that is most severely affected by the HIV epidemic. Among South African young people aged 15–24 years, >15% of young women and approximately 5% of young men are infected with HIV [
]. This great variation in HIV prevalence between Africa and the “West” has perplexed researchers since the beginning of the AIDS epidemic. Considering that most of the infections in sub-Saharan Africa are the result of heterosexual transmission, popular opinion has continued to foster the belief that the HIV epidemic in Africa is fueled by promiscuous sexual behavior [
Using data from nationally representative, population-based studies of young people aged 18–24 years in the US and SA, we aim to describe the sexual behaviors of young people in both countries so as to determine whether differences found in sexual behavior can explain the enormous disparity in the HIV epidemics observed in the two populations. This is the first study comparing nationally representative samples of young people in both a high and low HIV prevalence country.
Methods
Data were obtained from two nationally representative samples, the Reproductive Health and HIV Research Unit South African Youth Survey and the National Longitudinal Study of Adolescent Health (Add Health). The methods of both studies have been described in detail elsewhere (Appendix A, available online) [
]. Briefly, the Reproductive Health and HIV Research Unit South African Youth Survey is a nationally representative, cross-sectional household survey of youth aged 15–24 years in SA that was conducted between March 2003 and August 2003. The sample of the survey was identified using a three-stage, disproportionate, stratified design. The 2001 National Census was used as the sampling frame, and enumeration areas (EAs) were designated as the primary sampling units. Households within selected EAs were enumerated and one eligible youth per household was randomly selected to participate in the study. The response rate was 69%, with nonresponders more likely to be men, white, older, and to live in an urban area. The behavioral interview was an interviewer-administered questionnaire conducted in one of the nine languages. All questionnaires were translated from English into the local languages and then translated back again. HIV testing was conducted among all participants. To make the sample comparable with the Add Health wave III population, this analysis was restricted to young people aged 18–24 years (n = 7,548).
Add Health is a longitudinal cohort study in the US. Add Health follows a systematically drawn, nationally representative sample of young people who were attending school in the US and were in grades 7–12 between September 1994 and December 1995. Wave I was conducted between 1994 and 1995, wave II was conducted in 1996, and wave III in 2001 and 2002. Wave III participants, aged 18–24 years (n = 13,451), were all tested for HIV. This analysis used data from wave III which included all original (wave I) participants who were located and re-interviewed (77.4% response rate) for wave III [
]. Nonrespondents were more likely to be men, older age in wave I, black, urban, and from the Northeast. All interviews were conducted using computers; the respondents personally entered information that they considered more sensitive.
HIV testing in SA and the US was conducted using oral fluid samples collected by Orasure HIV-1 Oral Specimen Collection Device (Orasure Technologies Inc., Bethlehem, PA). Samples were tested for HIV-1/2 antibodies using the Vironostika University-Form II HIV-1/2 plus O MicroElisa System (bioMérieux, Durham, NC) for SA and tested for HIV-1 antibodies using the Oral Fluid Vironostika HIV-1 Microelisa System (Organon Teknika Corp, Durham, NC) for the American samples.
Statistical analyses
Key questions related to sexual health and HIV risk were identified in the South African questionnaire and comparable questions were further identified from Add Health (Table A1).
Descriptive statistics using unweighted counts and weighted proportions were calculated for key variables in both datasets. Analyses were conducted using STATA 9.0 (College Station, TX) allowing for sample strata, primary sampling units, and population weights, using appropriate techniques for analyzing a subpopulation within a survey sampling frame. This resulted in population-based estimates of behaviors among young people in each country, which are referred to as weighted estimates throughout this article. The weighted proportions of young people engaged in behaviors linked to risk of HIV in each country for descriptive comparisons are presented in this study. For some key measures (proportion of young people reporting ever having had sex, mean age of first sex, mean number of lifetime sex partners, use of condoms at last sex, mean partner age difference), two populations using a large sample t test approximations with unequal variance assumptions were compared on the basis of the observed mean and variance of the specific measures. However, interpretation of these tests must be made cautiously. Each population survey was designed with a distinct target population, supporting a qualitative, rather than a statistical comparison. Further, the sample sizes of these two studies were large, which substantially increased the power to demonstrate significant differences. Thus, we believe emphasis should be given to the actual estimates and whether the observed differences are meaningful from a public health perspective. Analyses were conducted for all youth, stratified by gender, and examined by age.
Results
Demographics
The mean age of the young women and men in SA were 20.7 and 20.6 years, respectively, whereas the mean age of the US young women and men was 21.5 and 21.6 years, respectively. As a marker of socioeconomic status, the reported educational level of the young person's mother was compared. In SA, 61.3% and 57.3% of young women and men as compared with 72.7% and 82.7% of young women and men in the US, respectively, reported that their mothers had completed high school or greater.
HIV prevalence
HIV prevalence in young women aged 18–24 years in SA was 207.5 per 1,000 (95% confidence interval [CI]: 168.60–246.47), whereas among young women in the US it was .87 per 1,000 (95% CI: .26–1.83). In young South African men aged 18–24 years, the HIV prevalence was 58.2 per 1,000 (95% CI: 47.35–69.10) and among young men in the US the prevalence was 1.06 per 1,000 (95% CI: .25–2.19).
Levels of sexual experience
Most of the young women aged 18–24 years in SA and the US reported having had vaginal sex (84.4% [95% CI: 82.3–86.4] and 87.9% [95% CI: 86.6–89.2], respectively; p < .001). South African women reported a later age of first sex as compared with their American counterparts, 17.4 years versus 16.5 years (p < .001). This is reflected by the fact that <65% of South African women reported having had sex by the age of 18 as compared with 71.4% of American women. In addition, early age of first sex (age: ≤14) was reported by 4.6% (95% CI: 3.6–5.7) of women in SA compared with 19.4% (95% CI: 17.7–21.1) of those in the US (Figure 1). Similar to their female peers, most of the young men in SA and the US belonging to this age group reported being sexually experienced, with young men in the US reporting being more sexually experienced than those in SA (86.0% [95% CI: 84.5–87.5] and 81.9% [95% CI: 79.2–84.6], respectively, p < .001). The average age at first sex for young men in SA and the US was 16.7 and 16.4 years, respectively, p = .04. This difference is noted when examining the distribution of age of coital debut; more men in the US report an early age of coital debut compared with men in SA (Figure 1).
Figure 1Age of first sex for young women and young men ages 18–24 years in SA and the US.
The mean number of lifetime sex partners reported by young women in SA was 2.4 for South African women and 5.7 for US women (p < .001), with ranges of 1–90 partners and 1–50 partners, respectively. As shown in Figure 2, more young women in SA than those in the US reported having only one lifetime partner; 35.1% (95% CI: 30.5–39.7) of women in SA reported having one lifetime partner compared with 21.1% (95% CI: 19.4–22.9) of women in the US. More American than South African young women reported having 10 or more lifetime partners. Among young men, the mean number of lifetime partners was 5.2 and 7.1 for South Africans and Americans, with ranges of 1–80 and 1–50, respectively, p < .01(Table 1). More young men in the US reported having >10 partners compared with men in SA (23.2% [95% CI: 21.4–25.0] vs. 12.5% [95% CI: 9.9–15.0]) (Figure 2).
Figure 2Number of lifetime sexual partners for sexually experienced young women and young men ages 18–24 years in SA and the US.
On average, the age of the most recent sexual partner for South African women was 4 years older, whereas American women had partners who were 2.6 years older (p < .01). Although <10% of young women in SA and the US have partners ≥10 years their senior (8.4% [95% CI: 7.0%–9.8%] and 5.1% [95% CI: 4.3–5.9, respectively]), overall more South African women had an older partner than American women. About 30% of American women (95% CI: 28.7–32.1) reported having a partner who was of same age or younger than themselves compared with only 8.2% (95% CI: 6.5%–10.0%) of South African women (Figure 3). Almost 90% (95% CI: 87.9%–92.2%) of South African and 75% of American men (95% CI: 72.9–76.6) reported that their most recent sexual partner was of same age or younger than themselves (Figure 3). Of those South African men who reported having a sexual partner of same age or younger, 14.4% (95% CI: 11.0%–17.9%) were of same age, 52.8% (95% CI: 49.0%–56.7%) were 1–2 years younger, 29.7% (95% CI: 26.9%–32.5%) were 3–5 years younger, and 3.1% (95% CI: 1.7%–4.5%) were >5 years younger. Of those American men reporting a sexual partner of same age or younger, 33.0% (95% CI: 30.4–35.6) were the same age, 49.0% (95% CI: 46.4–51.5) were 1–2 years younger, 17.0% (95% CI: 15.1–18.9) were 3–5 years younger, and 1.0% (95% CI: 0.4–1.5) were >5 years younger.
Figure 3Age difference with most recent partner for young women and young men ages 18–24 years in SA and the US.
Condom use at last sex was reported more by women in SA than those in the US; among sexually active youth, 45.4% (95% CI: 41.6%–49.2%) of women in SA and 36.1% (95% CI: 34.0–38.1) of women in the US reported using a condom at last sex (p < .01) (Table 1). Among sexually active young men, 58% (95% CI: 51.3%–64.7%) of young men in South Africa and 48.0% (95% CI: 45.6%–50.4%) of young men in the US reported using a condom at last sex (p < .001).
Discussion
Overall, the proportion of American youth reporting riskier sexual behavior (e.g., more sex partners, less condom use, and earlier age of coital debut) is consistently higher than their South African counterparts. The results of this study strengthens an accumulating body of evidence which finds that the sexual behaviors of individuals living in countries with generalized HIV epidemics are not at higher risk than those of individuals living in countries with low HIV prevalence epidemics [
]. Although sexual behavior(s) is a key determinant of HIV infection, factors that affect the probability of HIV transmission (i.e., viral load, sexually transmitted infections, circumcision) and the existing high background prevalence of HIV may be the key drivers for the continued heterosexual spread of HIV in SA. Thus, prevention programs should focus greater resources and attention to factors beyond individual level sexual behaviors.
One difference observed in the present study was that young South African women and men reported larger age differences with their most recent sex partners as compared with women and men in the US. Despite this, few women in SA or the US reported having a partner who was significantly older (i.e., ≥10 years). Age mixing between older and younger age groups has been cited as an important driver of the HIV epidemic, with infected older individuals acting as bridge populations whereby disease is spread to younger uninfected groups [
Factors controlling the spread of HIV in heterosexual communities in developing countries: Patterns of mixing between different age and sexual activity classes.
Philos Trans R Soc Lond B Biol Sci.1993; 342: 137-159
]. In addition, greater gender power disparities between young women and their older male partners make it more difficult for women to negotiate safer sex [
Cross-generational and transactional sexual relations in sub-Saharan Africa: A review of the evidence on prevalence and implications for negotiation of safe sexual practices for adolescent girls.
International Center for Research on Women,
Philadelphia, PA2001
]. Thus, it seems that even subtle age differences between partners may affect HIV risk, particularly if it results in sexual mixing with age groups that have a high prevalence of HIV infection.
South African men and women reported fewer lifetime sex partners compared with their US peers. Historically, there has been a general perception that African men are more promiscuous than their Western counterparts. However, cultural norms advocating and condoning multiple partnerships as instrumental to a successful male identity are common in both Africa and the West [
]. Similarly, a recent review of sexual behaviors from 59 countries found that the reporting of multiple sex partners was more common in developed than in developing countries [
]. Although major differences in number of partners between both countries are not apparent, it is possible that South African youth practice more concurrency than their US counterparts. We were unable to examine this issue. Concurrent partnerships seem to increase HIV transmission through populations to a far greater extent than serial monogamous relationships [
]. In fact, it was found that more US men and women reported their first sexual experience at age 14 or younger compared with their South African peers. Early age of first sex has been reported as a risk factor for HIV infection [
]. Although this is an important and laudable goal, it must be recognized that its effectiveness in preventing HIV in high prevalence countries may be quite limited [
]. This is salient given that many young people, particularly young women, do not control the terms and conditions of sexual relationships and many first sexual experiences are unwanted or forced [
Condom use at the most recent sex act was reported by more South African than US youth. Global trends of increasing condom use are mirrored in SA; the 1998 Demographic and Health Survey reported that only 16.6% of sexually active women used a condom at last sex compared with the proportion reported from this survey (45.4%) [
], young men reported using condoms more than their female peers; likely the result of gender power dynamics and the fact that men report having more casual partners than women and are more likely to use condoms during these sexual encounters [
In SA where at least one in 10 individuals is infected with HIV, the risk of coming into contact with an infected partner is far greater than in the US where the risk is approximately one in 1,000 (although the risk is skewed and higher for particular sub-groups of the population) [
]. This high prevalence of infection in the general South African population means that young people do not have to engage in high-risk behaviors (i.e., multiple partners, lots of unprotected sex) to be at risk for HIV infection. Certainly sexual behavior is an essential element of HIV risk; nevertheless, high-risk behavior may not be a prerequisite for HIV transmission.
Our findings support the hypothesis that factors which increase the probability of HIV transmission or acquisition might play a greater role in the continued spread of the epidemic in young susceptible populations than appreciated to date. Some of these factors were not measured in both surveys, but could partially explain disparities in the epidemics. High rates of STIs, in particular Herpes Simplex Type II Virus (HSV-2), have been found among youth in SA [
A community based study to examine the effect of a youth HIV prevention intervention on young people age 15-24 in South Africa: Results of a baseline survey.
Both surveys might be subject to social-desirability bias, resulting in over-reporting of some behaviors and under-reporting of others because they relied on self-reported sexual behavior. Both countries have different cultural contexts and norms that influence what is deemed socially desirable with regard to sexual behavior. In addition, the US survey was conducted using a mode that offered more privacy than the SA survey which could have resulted in US respondents feeling more comfortable reporting socially undesirable behaviors than their SA peers. Although some differences in reported behaviors between genders and countries may be a function of social desirability bias, certainly there are also true differences in behavior that are products of different cultures and contexts that encourage or dissuade particular sexual behaviors, and their reporting. Other limitations of these surveys include selection bias and nonresponse, which may result in the selected populations being at higher or lower risk than the total youth population in each country. As shown in Table A1, many variables of interest were assessed by asking similar questions, resulting in comparable covariates. Other concepts of interest, such as forced sex, were asked differently in the two questionnaires, limiting the ability to compare these self-reported behaviors across populations. Further, the prevalence of several potentially important risk factors (anal sex, same sex partner, injection drug use) was considered to be very low for inclusion in this analysis. In addition, we were unable to compare factors, such as concurrency, male circumcision, and HSV-2, which may explain some of the differences observed in epidemics between the two countries. We were unable to directly compare factors associated with prevalent HIV infection in each country because of the low number of HIV infections observed in the US sample.
Conclusion
Effective HIV prevention strategies demand an accurate perception of the spread of HIV. The results of this study demonstrate that the remarkable prevalence of HIV in young people in SA cannot be ascribed to exceptional risk taking behavior. Indeed, it seems clear that when HIV achieves the high population prevalence found in much of sub-Saharan Africa, “common” sexual behaviors lead to exceptionally high risk of HIV acquisition. Unique biological forces must be playing a role as well. Accordingly, successful HIV prevention in these populations will require extraordinary efforts that more clearly convey the risk involved in routine sexual behavior, as well as addressing contextual and/or structural and biological intervention strategies (e.g., topical microbicides or pre-exposure antiviral prophylaxis) still in urgent development.
Acknowledgments
The authors thank Dr Judy Auerbach for thinking and encouraging this comparison. This research uses data from Add Health, a program project designed by J. Richard Udry, Peter S. Bearman, and Kathleen Mullan Harris, and funded by a grant P01-HD31921 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, with cooperative funding from 17 other agencies. Special acknowledgment is due Ronald R. Rindfuss and Barbara Entwisle for assistance in the original design. Persons interested in obtaining data files from Add Health should contact Add Health, Carolina Population Center, 123 W. Franklin Street, Chapel Hill, NC 27516–2524 ([email protected]). No direct support was received from grant P01-HD31921 for this analysis.
The Reproductive Health and HIV Research Unit (RHRU) South African Youth Survey was funded by the Kaiser Family Foundation. Dr Pettifor's time was supported by the Developmental Awards Program of the National Institutes of Health NIAID. Sexually Transmitted Infections and Topical Microbicide Cooperative Research Centers (STI-TM CRC) grants to the University of Washington (AI 31448) and University of North Carolina (AI 31496).
Dr Pettifor had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. There are no conflicts of interest to report.
Appendix: A. Description of survey sampling and compatibility
Both surveys are nationally representative although they drew their samples from different populations of youth. The South African youth survey was household-based. The sample of the survey was identified using a three-stage, disproportionate, stratified design. The 2001 national census was used as the sampling frame and enumeration areas (EAs) were designated as the primary sampling unit (PSU), creating a nationally representative sample of youth ages 15–24 in all nine provinces of South Africa. Households within selected EAs were then enumerated and one eligible youth per household was randomly selected to participate in the study. The sample was weighted to be representative of young people aged 15–24 years in South Africa for gender, age, race, province, and geography type.
The Add Health survey was based on individuals who were enrolled in school during seventh to 12th grade in 1994, who were selected on the basis of a stratified random sample of high schools in the United States that included an 11th grade and an enrollment of at least 30 students. Stratification was based on region, urbanicity, school size and type, percent white and African American, grade span, and curriculum type. Subsequent waves of data collection were collected by locating youth at their homes, regardless of their continued enrollment in school. The sample was weighted to be representative of a nationally representative sample of American youth.
Because of the low high school attendance among South African youth, capturing them in their homes was the most appropriate method for obtaining a representative sample. In contrast, most American youth attend high school. In 1995, there were 50,502,000 American students enrolled in public and private schools and the drop out rate for 16–24 year olds was 12%. Therefore, using a school-based sample increased the likelihood of capturing a nationally representative sample. The surveys are thought to be compatible as they capture a group of youth that most represents the general population of that age in that country. As nonschool attendees may show riskier behaviors, their inclusion in the sample of US youth would likely skew estimates toward an even higher proportion of United States youth engaging in risky sexual behaviors.
Sources: U.S. Department of Education, National Center for Education Statistics. Digest of education statistics. Alexandria, VA: National Center for Education Statistics, 2005. (NCES 2006-030), Chapter 1.
U.S. Department of Education, National Center for Education Statistics. The condition of education. Alexandria, VA: National Center for Education Statistics, 2007. (NCES 2007-064), Indicator 23.
Table A1Table of selected questions from each survey used to define variables
Variable
RHRU: South Africa Question
Add health: United States Question
Ever had vaginal sex
Have you ever had vaginal sex with someone (i.e., to say when the penis was in vagina)? Remember to clarify: “This can have been done to you or you could have done it to someone” Yes/no
Have you ever had vaginal intercourse? Vaginal intercourse is when a man inserts his penis into a woman's vagina Yes/no
Age at coital debut
If yes to above: how old were you when you first did this?
How old were you the first time you had vaginal intercourse?
Number of lifetime sexual partners
How many different people have you had sexual intercourse with in your whole lifetime? Remember that sex is defined as anal or vaginal sex
With how many partners have you ever had vaginal intercourse, even if only once?
Age difference with last sexual partner
What was your age when you first had sex with most recent partner? What was your partner's age when you first had sex?
For each relationship: “How old were you when your sexual relationship with partner began?” How old was she/he?
Condom use at last sex act (among those who have ever had sex)
The last time you had sexual intercourse, did you use a condom? Yes/no
The most recent time you had vaginal intercourse did you/your partner use a condom? Yes/no
Factors controlling the spread of HIV in heterosexual communities in developing countries: Patterns of mixing between different age and sexual activity classes.
Philos Trans R Soc Lond B Biol Sci.1993; 342: 137-159
Cross-generational and transactional sexual relations in sub-Saharan Africa: A review of the evidence on prevalence and implications for negotiation of safe sexual practices for adolescent girls.
International Center for Research on Women,
Philadelphia, PA2001
A community based study to examine the effect of a youth HIV prevention intervention on young people age 15-24 in South Africa: Results of a baseline survey.
Pettifor et al's recent study concludes that “the remarkable prevalence of HIV in young people in South Africa cannot be ascribed to exceptional risk taking behavior” [1]. This and the accompanying editorial [2] argue that behavioral change campaigns have “failed,” and that more emphasis needs to be placed on biological interventions.
Pettifor et al. recently compared sexual behavior self-reports and HIV prevalence in nationally representative samples of young people in South Africa (SA) and the United States [1]. They concluded that “young people in the US report riskier sexual behaviors than young people in SA, despite the much higher prevalence of HIV infection in SA. Factors above and beyond sexual behavior likely play a key role in ongoing transmission of HIV in South African youth, and thus should be urgently uncovered to develop maximally effective prevention strategies” (p.
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