Sexual Behaviour Change in Countries with Generalised HIV Epidemics? Evidence from Population-Based Cohort Studies in Sub-Saharan Africa

This paper presents 10 recent analyses of sexual behaviour data from longitudinal studies in 5 countries - Uganda, Tanzania, Malawi, Zimbabwe, and South Africa - experiencing different sizes and stages of the HIV epidemic. The purpose is to highlight appropriate HIV prevention methods and to encourage better analysis and presentation of sexual behaviour data, especially as they relate to HIV and HIV prevention.

This investigation is based on the understanding that, though adoption of safer sexual behaviour is still the main message of most national HIV prevention programmes, ecological studies have failed to find associations between risk behaviour and the prevalence of HIV or other sexually transmitted infections (STI), and scientific trials show no evidence for a population-level effect of behavioural interventions. As the authors explain here, measurement and comparison of sexual behaviour is challenging due, for example, to variations in social desirability and other reporting bias. Thus, limitations in the reliability and consistency of the methods used to collect and analyse data on sexual behaviour, particularly when made across time or space, could contribute to these apparently contradictory findings.

As detailed here, the Demographic and Health Surveys (DHS) conducted in many African countries have provided data on age at first sex. Survival analysis has been used to analyse such data because it reportedly allows comparison of easily understood measures based on the cumulative risk of becoming sexually active. This type of analysis is "useful, not only for spatial and temporal comparisons but also because it can give easily comparable hazard ratios for different exposures." Survival methods have also been used to look at age at first marriage in Zimbabwe. The authors cite a range of papers noting that "unreliable or inconsistent reporting of age at first sex and age at first marriage make little difference to the levels and trends of the estimated summary measures, suggesting that reporting anomalies introduce noise rather than bias to the patterns observed at the population level." The authors deem this finding an important "vote of confidence in cross-sectional studies such as DHS which cannot identify or measure the effects of inconsistent reporting from one round to the next."

Findings from cohort studies are presented in order to "provide some reassurance as to the reliability, at the aggregate level, of data collected on sexual behaviour in cross-sectional and longitudinal population surveys." Reviewing these studies, the authors reflect on a consensus that emerges: While only considerable delays in onset of sexual activity could plausibly contribute to declines in HIV prevalence, "early sexual debut is an important individual-level risk factor for STIs including HIV infection...and also for teenage pregnancy." On the other hand, the authors cite a paper arguing that countries where men and women marry later tend to have larger HIV epidemics owing to greater premarital sexual activity. "From this perspective, the finding that the interval between sexual debut and marriage may be widening in several countries, as a result of earlier sexual debut and/or delayed marriage, must be a concern for policymakers."

In conclusion, the authors assert that "Increased availability, from serial DHS and from cohort studies, of reliably and consistently measured data on sexual behaviour, linked to data on HIV infection and the coverage of prevention and treatment programmes, could contribute to improved evaluation and enhancement of these programmes."