The median AFS for young women and men was 18.5 years and 19.2 years, respectively. This is consistent with Bakilana’s estimate of 18 years for South African women using 1998 DHS data and a survival analysis approach.14
Bakilana found that South African women tended to enter into sexual relations later than Tanzanians and more or less at the same age as Zimbabweans. Similarly, Hallett et al
found that the median AFS for women was 18 years and for men was 19 years in rural Zimbabwe in 2000.9
Different methods for summarising AFS will give slightly different estimates.21
Our study design selected only virgins aged 12–25 years at the beginning of the study period. By excluding those who debuted early, we may therefore overestimate the median AFS. In contrast, median AFS estimates in a 2003 South African nationally representative survey by Pettifor et al3
(16 years for men and 17 years for women) may have been underestimated, given that AFS was estimated among 15–24-year-olds who had ever had sex at the time of the cross-sectional survey. Our estimate is, however, similar to the median AFS of 18 years for both sexes reported from the Nelson Mandela HSRC national survey (2002), based on a larger age group of 15–49-year-olds.4
The sex differential in AFS between men and women in our study is also consistent with other South African data showing that men had partners aged, on average, 1 year younger than themselves, while women had partners who were on average 4 years older.3
Time-to-event (Cox) analyses were used because it allows the inclusion of individuals who did not sexually debut during the observation period, thereby comparing the number of individuals at risk (virgins) in each group at multiple points in time rather than excluding those who remain virgins (a biased analysis). However, the hazard ratios estimated in these Cox models do not translate directly into information about the actual age at first sex, unless the data are fit to an underlying parametric survival distribution.
The longitudinal data available in ACDIS provide an opportunity to examine AFS and its determinants, ensuring temporality of the determinants relative to first sex as well as permitting the updating of these factors during the time that an individual remained at risk of sexual debut. We found several factors significantly associated with AFS in men and women, with the majority being important for one sex but not the other.
School attendance was significantly associated with later sexual debut among both men and women. The fact that school attendance needed to be considered separately for women aged <18 years, 18–21 years and 21+ years in order to fulfil the proportional hazards assumption suggests that the protective effect of school is not constant in women and, in part, depends on age. Other studies also report a strong association between school attendance and later AFS in young women.11
Like us, other authors note the difficulty in disentangling the temporality of pregnancy and school non-attendance between rounds of data collection. We found no association of AFS with grade-for-age among women. In contrast, both school attendance and being behind in terms of grade-for-age were significantly associated with a later AFS for young men. We are unaware of previous studies examining this association in young men. A review by Hargreaves and Boler found no “striking gender differences” in terms of the impact of education on HIV vulnerability which included early AFS.11
Our results are consistent with other literature that suggests the school environment is associated with later first sex in men and women. The additional suggestion that being behind in school has a protective effect for men warrants further investigation. Notably, 49% of the men were
2 years behind their grade-for-age compared with 31% of the women in these analyses.
Many studies have focused on orphanhood and its impact on sexual behaviour outcomes,12 13 22 23
education and household socioeconomic status.24 25
We found maternal death was significantly associated with earlier AFS for women, in the same way that paternal death was for young men. The ACDIS data enable us to explore whether parental comembership of a young person’s household is associated with AFS. Mother’s membership of the same household significantly delayed AFS of young men, after adjusting for father’s survival status and other factors. This positive influence on AFS is consistent with observations in Côte d’Ivoire26
and the USA.27
In the study population, young people were much more likely to be a member of the same household as their mother than their father.28
- For both sexes, school attendance was significantly associated with later age at first sex (AFS).
- For both sexes, periurban residence (versus rural), ever use of alcohol and knowing someone who had HIV were associated with earlier AFS.
- Other factors significantly associated with AFS were important for one gender only, including maternal death for women and paternal death for men.
- Given the influence of individual, household and community-level factors, a multisectorial approach to prevention and targeting in youth programmes is recommended.
Religious affiliation was significantly associated with AFS in women but not in men. Religion was also shown to be a predictor of AFS in a study in Nigeria.10
Whether this reflects varying levels of religiosity between different churches, the type of messages about sex and institutional pressure within church or peer norms within a church-based social network in delaying first sex is unclear.27
In many African populations, first marriage is an important determinant of AFS, particularly for women. However, in our analysis, so few young men and women were married by the age of 25 years that it was not possible to explore marriage as a determinant of AFS. Data from ACDIS in 2006 indicate that only 7% of 25–29-year-old women had ever married, while only 1% of men of the same age group had ever married.29
For both sexes, AFS was significantly associated with place of residence, ever use of alcohol and knowing at least one person who had HIV. The association of alcohol use with earlier AFS has been observed in some non-African populations.27 30
Access to alcohol may also reflect the social environment in which these young people live, one that may have facilitated earlier sexual debut by introducing possible sexual partners and opportunities. The data do not specify whether alcohol was used at the time of first sex.31
Although ever having smoked was a rare event (5% in those with non-missing data), it was correlated with alcohol use and was an independent risk factor of earlier AFS among men, even after adjustment for ever use of alcohol and other factors. Smoking and alcohol use may identify young “risk takers”, people who are also more likely to explore sexual activity early. Furthermore, living in a more rural rather than a periurban area was associated with later AFS in men and women. The periurban area is densely, often informally, settled. These findings suggest that there may be a constellation of community-level factors that influence the timing of first sex.
Knowing at least one person with HIV was associated with significantly earlier AFS. This may disappoint those hoping that first-hand experience of HIV might delay sexual debut. However, despite the extensive epidemic in this area,1 2
the majority of young people reported knowing nobody in 2003/4 with HIV. This may suggest a lack of disclosure and denial, mirrored by the evenly split responses by both young men and women as to whether HIV is a danger to their community.
The analysis of early first sex (defined as before age 17 years) showed that the variables identified as important factors in the overall analysis for men and women were generally statistically significant in the subgroup analyses as well. This may not be surprising, given the assumption of proportional hazards over time (ie, age) underlying the overall analysis. However, the fact that these factors were significant in this less powered analysis may suggest that efforts to delay first sex can use the same prevention messages to target both those aged under 17 years and those under 25 years of age.
Limitations of the study
Almost 25% of the men in these analyses had not sexually debuted by the age of 25 years. This could in part be an artifact of data collection since the male—but not female—surveys identified men who had “never had sex” from the question “How old were you when you started to have sex?” rather than directly asking about ever having sex. Generally, sexual behaviour surveys are subject to social desirability bias32
and inconsistent reporting of AFS for other reasons.33
We were able to cross-check internal consistency using questions on paternity and recent sexual partnerships.
In women, missing data on maternal survival was associated with earlier AFS in the multivariable models. However, these data were only missing for 3% of the person time at risk and may be a proxy for recent maternal death or lack of maternal involvement. For both sexes, missing HIV knowledge data generally reflect a younger age in 2003 since the lower limit for participation was 15 years in all surveys. However, the significant association of these missing data with earlier AFS may also reflect unmeasured confounding in selection into later survey rounds or may be due to chance. In addition, our inability to update information about alcohol use, smoking and HIV knowledge during the period means that, for some individuals, the data may not reflect knowledge and behaviour at the time of sexual debut.
Studies have shown that the risk of HIV infection is lower among women who begin sexual activity later,34 35
and that sex education and HIV education interventions can successfully delay sexual debut in developing countries.36
Our findings provide additional insights about the timing and factors associated with sexual debut in a population experiencing a severe HIV epidemic. The specific vulnerabilities of youth at the individual, household and community level call for a multisectorial approach to prevention programmes targeting youth to reduce HIV risk,37 38
as well as the targeting of the timing of interventions (eg, while young people are still in school).