The generational effect on age disparate partnerships and the risk for human immunodeficiency virus and sexually transmitted infections acquisition

Couple-level determinants of syphilis infection among heterosexual married couples of reproductive age in Guangdong Province, China: A population-based cross-sectional study

Background

Syphilis remains a major public health problem worldwide, and its prevention requires knowledge of factors that go beyond the individual-level. However, most syphilis-related studies have focused on individual-level and regional-level factors, neglecting couple-level factors. Thus, this study aimed to explore couple-level determinants of syphilis infection among heterosexual married couples.

Methods

This population-based cross-sectional study used data from heterosexual married couples who participated in the National Free Preconception Health Examination Project in Guangdong Province, China during 2014-2019. The syphilis infection was tested by the rapid plasma reagin test. Couple-level data were obtained by combining information provided by the man and woman living in the same household. Multivariate logistic models were employed to explore the couple-level determinants of syphilis infection by gender after adjusting for potential confounders.

Results

A total of 1,755,156 couples were recruited in this analysis. The seroprevalence was 0.25% (95%CI: 0.24-0.25%) and 0.26% (95%CI: 0.25-0.27%) among men and women, respectively. The median age was 28.0 (interquartile range, IQR: 25.0-31.0) years, and the median duration of marriage was 0.2 (IQR: 0.0-2.5) years. After adjusting for individual and regional-level variables, duration of marriage was a protective factor for syphilis infection in men (adjusted odds ratios, AOR: 0.97; 95% CI: 0.96-0.98) and women (AOR: 0.95, 95% CI: 0.94-0.96). The age gap and the difference in education level between the husband and wife were associated with syphilis infection, but these associations were somewhat different between men and women. Condom use was negatively associated with syphilis infection in men (AOR: 0.77; 95% CI: 0.70-0.84) and women (AOR: 0.77, 95% CI: 0.71-0.84). Our results also showed that couple mobility and the number of children were not statistically significant determinants of syphilis infection among heterosexual married couples.

Conclusion

This study contributes to a more comprehensive understanding of syphilis outcomes in individuals in the context of marriage in China. Several couple-level factors are indeed associated with syphilis infection, but these associations differ between men and women. Couple-based strategies that engage both women and men and efforts to promote condom use among heterosexual married couples need to be developed and further evaluated for syphilis prevention.

Etiological Surveillance of Vaginal Discharge Syndrome in South Africa: 2019 to 2020

BACKGROUND

The syndromic management of vaginal discharge syndrome (VDS) is challenging because of the prevalence of mixed infection with sexually transmitted infection (STI) pathogens and non-STI causes, such as bacterial vaginosis and candidiasis (CA). We aimed to determine the relative prevalence of VDS etiologies in women presenting to sentinel primary health care clinics in South Africa. Secondary objectives were to ascertain the predictive value of speculum findings for the presence of STI pathogens and the proportion of women presenting with clinical features of CA who had identifiable yeast on vaginal smear microscopy.

METHODS

Consecutive, consenting women with complaints of abnormal vaginal discharge were enrolled between January 1, 2019, and December 31, 2020. Genital discharge swab and blood specimens were collected and transported to a central STI reference laboratory in Johannesburg.

RESULTS

A total of 364 women were enrolled at 3 sentinel sites. Bacterial vaginosis was the most common cause of VDS (163 of 361 [45.2%]; 95% confidence interval [CI], 40.1%-50.3%); however, a significant proportion had STI coinfection (71 of 163 [43.6%]; 95% CI, 35.8%-51.5%). The predominant STI etiology was Chlamydia trachomatis (73 [20.2%]; 95% CI, 16.4%-24.7%). An abnormal speculum finding had poor predictive value for STIs, and Gram stain microscopy showed yeast in only 37.2% of vaginal smears from women with CA symptoms.

CONCLUSIONS

Bacterial vaginosis is the predominant cause of VDS in South Africa; however, STI coinfection is common. Clinical findings are poorly predictive of STI etiologies or candidiasis; therefore, a rapid and accurate STI point-of-care test would be useful in optimizing VDS management.

Sexual partnership concurrency and age disparities associated with sexually transmitted infection and risk behavior in rural communities in Kenya and Uganda

OBJECTIVES

We examined sex-specific associations of partner age disparity and relationship concurrency with Neisseria gonorrhoeae and/or Chlamydia trachomatis (NG/CT) infection, higher-risk relationships, and condom use as proxies for HIV risk.

METHODS

Data were collected in 2016 from 2179 adults in 12 communities in Uganda and Kenya. Logistic regression models examined associations of age disparity and relationship concurrency with NG/CT infection, condom use, and higher-risk (commercial sex and other higher-risk) relationships in the past 6 months, controlling for covariates.

RESULTS

Partner age and relationship concurrency were associated with NG/CT infection in women but not men. Relative to women in age-disparate relationships, women in both age-disparate and age-homogeneous relationships had higher odds of NG/CT infection (adjusted odds ratio [aOR]=3.82, 95% confidence interval [CI]: 1.46-9.98). Among men and women, partnership concurrency was associated with higher-risk partnerships. In addition, relative to those with a single age-homogeneous partner, those with concurrent age-homogeneous partners had higher odds of condom use (men: aOR=2.85, 95% CI: 1.89-4.31; women: aOR=2.99, 95% CI: 1.52-5.89). Concurrent age-disparate partnerships were associated with condom use among men only (aOR=4.02, 95% CI: 2.54-6.37).

CONCLUSION

Findings underscore the importance of targeted HIV prevention efforts for couples in age-disparate and concurrent relationships.

Quantifying Vulnerabilities of Single Women and Sexually Transmitted Infections in South Africa (2002-2016): Is It Getting Better (or Worse)?

Curable sexually transmitted infections (STIs) affect millions of people across the world. Besides unacceptably high HIV rates, South Africa also has the highest burden of STIs in the world. The aim of the study was to investigate temporal changes in STI incidence rates using the data from ~ 10,000 women who enrolled in several HIV prevention trials, KwaZulu-Natal, South Africa (2002-2016). We particularly focused on the changes in distribution of the most influential factors and their population-level impacts on STI incidence rates over time. Characteristics of the women were compared across the study periods: 2002-2004, 2005-2008, 2009-2011, and 2012-2016. Besides multivariable Cox regression models, population attributable risks were calculated for the significant factors. Despite the significant progress in prevention, testing, and treatment programs, infection rates increased substantially from 13.6 to 20.0 per 100 person-year over the study period. Our findings provided a compelling evidence for single/non-cohabiting South African women to be the most vulnerable population who consistently and substantially contributed to increasing STI rates during the 15 years of study duration (PAR%: 44%-47%). We also highlighted the impact of women's lack of knowledge related to their partner, using injectable contraceptives, less parity, and baseline STI positivity which were increased substantially over time. Our findings suggest that a significant proportion of STIs could be prevented by targeting single/non-cohabiting. These results may provide guidance in developing more effective STI prevention programs by targeting women at highest risk of infections and delivering more realistic messages.

Characteristics of women who use hormonal contraceptives and their population-level impacts on HIV infection in a cohort of South African women (2002-2016)

PURPOSE

Women's choice of contraceptive can have broader implications and may play a significant role in shaping their sexual practices. We aim to identify the characteristics of women who use hormonal injectables and those at high-risk of HIV infection. We also quantify the population-level impact of their shared characteristics on HIV incidence rates.

MATERIALS AND METHODS

Data from 9948 women who enrolled in six-HIV prevention trials conducted in South Africa (2002-2016) were included. We used logistic and Cox regression models and estimated the population-level impact of the use of injectables on HIV incidence in the multifactorial-model setting.

RESULTS

Using hormonal injectables were associated with increased risk of HIV infection (adjusted Hazard ratio (aHR):1.51, 95% CI:1.22, 1.86). At the population level less than 20% of the infections were associated with injectable contraceptives among younger women (i.e., less than 35 years of age). Factors including being single/not-cohabiting, using condoms at last sex, partner-related factors, and STI diagnosis were all identified as shared characteristics of women who preferred using hormonal injectables and those at high-risk of HIV infection. At the population level, these factors were associated with more than 50% of the infections among women younger than 35 years of age.

CONCLUSIONS

Our analysis presented evidence for the overlapping characteristics of the women who used hormonal injectables and those at high-risk of HIV infection. These findings reinforce the importance of comprehensive contraceptive counselling to women about the importance of dual protection, such as male condoms and hormonal contraceptives use.

Assessing the uncertainty around age-mixing patterns in HIV transmission inferred from phylogenetic trees

Understanding age-mixing patterns in Human Immunodeficiency Virus (HIV) transmission networks can enhance the design and implementation of HIV prevention strategies in sub-Saharan Africa. Due to ethical consideration, it is less likely possible to conduct a benchmark study to assess which sampling strategy, and sub-optimal sampling coverage which can yield best estimates for these patterns. We conducted a simulation study, using phylogenetic trees to infer estimates of age-mixing patterns in HIV transmission, through the computation of proportions of pairings between men and women, who were phylogenetically linked across different age groups (15-24 years, 25-39 years, and 40-49 years); and the means, and standard deviations of their age difference. We investigated also the uncertainty around these estimates as a function of the sampling coverage in four sampling strategies: when missing sequence data were missing completely at random (MCAR), and missing at random (MAR) with at most 30%-50%-70% of women in different age groups being in the sample. The results suggested that age-mixing patterns in HIV transmission can be unveiled from proportions of phylogenetic pairings between men and women across age groups; and the mean, and standard deviation of their age difference. A 55% sampling coverage was sufficient to provide the best values of estimates of age-mixing patterns in HIV transmission with MCAR scenario. But we should be cautious in interpreting proportions of men phylogenetically linked to women because they may be overestimated or underestimated, even at higher sampling coverage. The findings showed that, MCAR was the best sampling strategy. This means, it is advisable not to use sequence data collected in settings where we can find a systematic imbalance of age and gender to investigate age-mixing in HIV transmission. If not possible, ensure to take into consideration the imbalance in interpreting the results.

Determinants of intergenerational sexual relationships and HIV risk among South African women outpatients in Gauteng

Age-discrepant sexual relationships may place women at risk for HIV infection in South Africa. Results are based on medical records and case-control interview data of 889 sexually experienced women outpatients aged 15-29 in a Gauteng township. Women with partners at least ten years older (intergenerational) show an elevated chance of having an early sexual debut, concurrent and transactional partners, and intimate partner violence. Hardship during childhood including parental loss, food insecurity and abuse are related to age asymmetric relationships. HIV is two times more likely (aOR=1.96) with an intergenerational partner. Transactional sex increases the odds of HIV independently (aOR=1.76) as does intimate partner violence (aOR=1.6). To the extent that transactional and intergenerational sex overlap the chance of contracting HIV increases more than two-fold (uOR=4.57). Girls (15-19) with intergenerational partners face the highest chance of HIV (uOR=8.55) compared to other age groups. They are also five times more likely than controls to have lived with a cross-age partner. Our findings indicate there are multiple pathways emanating from childhood leading to women's choice of intergenerational partners, and the link to HIV is strongest among the youngest women.

Risk of HIV infection among adolescent girls and young women in age-disparate relationships in sub-Saharan Africa

OBJECTIVE

To determine the association between age-disparate relationships and risk of HIV infection among adolescent girls and young women (AGYW) aged 15-24 years.

DESIGN

Systematic review and meta-analysis of published studies until January 5, 2020 in sub Saharan Africa (SSA).

METHODS

We searched several electronic databases, grey literature, and hand searched reference list of included studies to identify eligible studies for data abstraction. We assessed the quality of included studies using Newcastle-Ottawa Scale for nonrandomized studies. The DerSimonian-Laird random effects model was used to pool the overall results using risk ratios (RR), presented in a forest plot with 95% confidence interval (CI) and predictive interval. Heterogeneity was assessed with Cochrane's Q-test and quantified with I values. Publication bias was checked with funnel plots and Egger's test.

RESULTS

We included 24 studies with an overall sample size of 33 390. Data show that age-disparate relationships were significantly associated with unprotected sexual intercourse (pooled RR, 1.57; 95% CI, 1.34-1.83; 95% predictive interval, 1.22-2.02), and higher risk for HIV infection (pooled RR, 1.39; 95 CI, 1.21-1.60; 95% predictive interval, 0.80-2.42). Studies included in pooling risk of unprotected sexual intercourse were largely homogeneous (I-value= 0.0, P = 0.79) whereas those for HIV infection were heterogeneous (I- value = 89.0%, P < 0.01). We found no publication bias and no study influenced the meta-analytic results.

CONCLUSION

Age-disparate relationships among AGYW are associated with increased risk of unprotected sexual intercourse and HIV infection in SSA. HIV prevention interventions should target this sub-population.

Temporal trends in sexual behaviours and their impacts on HIV incidence among South African women: 2002-2016

South Africa has the highest number of HIV infected individuals in the world. The primary objective of the current study was to describe temporal changes in HIV incidence rates using the data from 9,948 women who enrolled in one of the six HIV prevention trials conducted in KwaZulu-Natal, South Africa. Characteristics of the study population were presented and compared across the four study periods: 2002-2004, 2005-2008, 2009-2011 and 2012-2016. HIV infection rates increased from 6.2 to 9.3 per 100 person-year over the 15 years. These rates were as high as 14 per 100 person-year among women younger than 20 years age. Being single/not cohabiting, using injectable contraceptives, having less than two children, and diagnosed with STI(s) were associated with increased risk of HIV infection. These four factors were associated with 71%, 75%, 80% and 88% of the HIV seroconversions in four study periods. As the research continues to find ways of controlling the spread of the infections, quantifying the temporal trends in risk factors and their population-level impacts on HIV infection may have significant implications. This information may assist in developing effective counselling and education programs by targeting the sexually active single women and delivering more realistic messages.

Recently formed age-disparate partnerships are associated with elevated HIV-incidence among young women in South Africa

OBJECTIVE

Cross-sectional and cohort studies draw different conclusions on whether age-disparate partnerships increase HIV-acquisition risk for young women. We investigated whether age-disparities were associated with HIV-infection risk early in relationships. This could result in the exclusion of women who seroconverted during high-risk age-disparate partnerships from cohort studies of HIV incidence - which exclude HIV-positive women - and explain null findings in these studies.

DESIGN

Prospective cohort study.

METHODS

We used data on 15-24-year-old, HIV-negative women in heterosexual partnerships (N = 830) in KwaZulu-Natal, South Africa. The association between age-disparate partnering (i.e., male partner ≥5 years older) and subsequent HIV seroconversion was assessed using Cox hazard models. We examined heterogeneity in HIV-acquisition risk by duration of partnership (defined by quartiles) at cohort enrolment.

RESULTS

During 1139 person-years (mean: 1.4 years) of follow-up, 54 (6.5%) women seroconverted, a weighted HIV-incidence estimate of 4.41/100 person-years [95% confidence interval (CI): 3.30-6.06]. HIV-acquisition risk did not differ significantly between women in age-disparate vs. age-similar partnerships (adjusted hazard ratios: 1.10, 95% CI: 0.55-2.21). However, for women in the shortest partnership quartile (<1.09 years) at baseline, risk of HIV seroconversion was higher for women in age-disparate partnerships (adjusted hazard ratios: 3.13, 95% CI: 1.02-9.65, P = 0.047). HIV acquisition was not statistically different by partnership type among women in longer partnerships.

CONCLUSION

The association between age-disparate partnerships and HIV-acquisition risk is evident early in young women's relationships. Results provide a potential explanation for null findings in cohort studies, whose research designs may exclude women in such partnerships, and affirms the elevated risk of HIV acquisition for young women in age-disparate relationships.

Brief Report: Age-Disparate Relationships and HIV Prevalence Among Never Married Women in Rakai, Uganda

BACKGROUND

Age-disparate relationships are associated with increased HIV prevalence. We determined whether the frequency of age-disparate relationships in never married women changed over time and whether they are associated with HIV prevalence in Rakai, Uganda.

METHODS

A total of 10,061 never married women, aged 15-49 years, in the Rakai Community Cohort Study provided information on the age of their male sexual partners from 1997 to 2013. Logistic regression was used to assess trends in age-disparate relationships (≥5 years) between never married women and their male partners. Log-binomial regression was used to estimate adjusted prevalence ratios (adjPR) of HIV prevalence associated with age-disparate relationships.

RESULTS

Two thousand nine hundred ninety-nine women (30%) had a male partner ≥5 years older, which remained stable over time. The prevalence of HIV among women in age-disparate relationships was 14%, 10% for women in relationships with men 0-4 years older (adjPR 1.36, 95% confidence interval: 1.22 to 1.53) not controlling women's age; however, after age adjustment, the impact of age-disparate relationships on HIV prevalence was attenuated. Age-disparate relationships were associated with increased HIV prevalence among women aged 15-17 years (adjPR 1.83, 95% confidence interval: 1.10 to 3.17), but not in other age groups.

CONCLUSIONS

The frequency of age-disparate relationships among never married women was unchanged over a 15-year period in Rakai, Uganda. Age-disparate relationships were associated with increased HIV prevalence among adolescents aged 15-17 years, but not older women.

Investigating spatial disparities in high-risk women and HIV infections using generalized additive models: Results from a cohort of South African women

OBJECTIVE

We identified the geographical clustering of HIV as well as those at highest risk of infection using a decade long data (2002-2012) from KwaZulu-Natal, South Africa.

METHODS

A total of 5,776 women who enrolled in several HIV prevention trials were included in the study. Geo-coded individual-level data were linked to the community-level characteristics using the South African Census. High-risk women were identified using a risk scoring algorithm. Generalized additive models were used to identify the significant geographical clustering of high-risk women and HIV.

RESULTS

Overall, 60% of the women were classified as high risk of HIV. HIV infection rates were estimated as high as 10 to 15 per 100 person year. Areas with high rates of HIV infections were spatially clustered and overlapped particularly in the Northern part of Durban.

CONCLUSION

Targeting multifactorial and complex nature of the epidemic is urgently needed to identify the "high transmission" areas.

The role of age-mixing patterns in HIV transmission dynamics: Novel hypotheses from a field study in Cape Town, South Africa

BACKGROUND

Age-disparate relationships are thought to put young women at increased risk of HIV, though current evidence is inconclusive. Studying population-level age-mixing patterns as well as individual-level measures of age difference variation may provide insight into the persistence and magnitude of the epidemic in South Africa.

METHODS

We used data from a survey in Cape Town (n = 506) to describe age-mixing dynamics in the four population strata of HIV negative and HIV positive male and female participants. Mixed-effects models were used to calculate the average increase in partner age for each year increase in age of participant, the average partner age for 15 year olds, and the between-subject and the within-subject standard deviation of partner ages. We conducted 2000 bootstrap replications of the models. Using negative binomial models, we also explored whether HIV status was associated with participants having a larger range in partner ages.

RESULTS

HIV positive women had large variability in partner ages at the population level, and at the individual level had nearly three times the expected range of partner ages compared to HIV negative women. This pattern may increase the potential for HIV transmission across birth cohorts and may partially explain the persistence of the epidemic in South Africa. Young men, who have been previously absent from the age-disparity discourse, also choose older partners who may be putting them at increased risk of HIV infection due to the high HIV prevalence among older age categories of women.

Partner age differences and associated sexual risk behaviours among adolescent girls and young women in a cash transfer programme for schooling in Malawi

Background

Age disparities in sexual relationships have been proposed as a key risk factor for HIV transmission in Sub-Saharan Africa, but evidence remains inconclusive. The SIHR study, a cluster randomised trial of a cash transfer programme in Malawi, found that young women in the intervention groups were less likely to have had a sexual partner aged 25 or older, and less likely to test positive for HIV and HSV-2 at follow-up compared to control groups. We examined the hypotheses that girls in the intervention groups had smaller age differences than control groups and that large age differences were associated with relationship-level HIV transmission risk factors: inconsistent condom use, sex frequency, and relationship duration.

Methods

We conducted an analysis of schoolgirls in the Schooling, Income, and Health Risk (SIHR) study aged 13-22 at baseline (n = 2907). We investigated the effects of study arm, trial stage and participant age on age differences in sexual relationships using a linear mixed-effects model. Cumulative-link mixed-effects models were used to estimate the effect of relationship age difference on condom use and sex frequency, and a Cox proportional hazard model was used to estimate the effect of relationship age difference on relationship duration. We controlled for the girl’s age, number of partners, study group and study round.

Results

Girls receiving cash transfers, on average, had smaller age differences in relationships compared to controls, though the estimated difference was not statistically significant (− 0.43 years; 95% CI: -1.03, 0.17). The older the participant was, the smaller her age differences (− 0.67 per 4-year increase in age; 95% CI: -0.99, − 0.35). Among controls, after the cash transfers had ended the average age difference was 0.82 years larger than during the intervention (95% CI: 0.43, 1.21), suggesting a possible indirect effect of the study on behaviour in the community as a whole. Across treatment groups, larger age differences in relationships were associated with lower levels of condom use, more frequent sex, and longer relationship durations.

Conclusions

Cash-transfer programmes may prevent HIV transmission in part by encouraging young women to form age-similar relationships, which are characterised by increased condom use and reduced sex frequency. The benefits of these programmes may extend to those who are not directly receiving the cash.

Electronic supplementary material

The online version of this article (10.1186/s12889-018-5327-7) contains supplementary material, which is available to authorized users.

Effect of Schooling on Age-Disparate Relationships and Number of Sexual Partners Among Young Women in Rural South Africa Enrolled in HPTN 068

BACKGROUND

Attending school may have a strong preventative association with sexually transmitted infections among young women, but the mechanism for this relationship is unknown. One hypothesis is that students who attend school practice safer sex with fewer partners, establishing safer sexual networks that make them less exposed to infection.

SETTING

We used longitudinal data from a randomized controlled trial of young women aged 13-20 years in the Bushbuckridge district, South Africa, to determine whether the percentage of school days attended, school dropout, and grade repetition are associated with having a partner 5 or more years older (age-disparate) and with the number of sexual partners in the previous 12 months.

METHODS

Risks of having an age-disparate relationship and number of sexual partners were compared using inverse probability of exposure weighted Poisson regression models. Generalized estimating equations were used to account for repeated measures.

RESULTS

Young women who attended fewer school days (<80%) and who dropped out of school were more likely to have an age-disparate relationship (risk difference 9.9%, 95% confidence interval [CI]: 3.9% to 16.0%; risk difference (%) dropout 17.2%, 95% CI: 5.4% to 29.0%) and those who dropped out reported having fewer partners (count difference dropout 0.343, 95% CI: 0.192 to 0.495). Grade repetition was not associated with either behavior.

CONCLUSION

Young women who less frequently attend school or who drop out are more likely to have an age-disparate relationship. Young women who drop out have overall more partners. These behaviors may increase the risk of exposure to HIV infection in young women out of school.

Sexual partnership age pairings and risk of HIV acquisition in rural South Africa

OBJECTIVE

To quantify the contribution of specific sexual partner age groups to the risk of HIV acquisition in men and women in a hyperendemic region of South Africa.

DESIGN

We conducted a population-based cohort study among women (15-49 years of age) and men (15-55 years of age) between 2004 and 2015 in KwaZulu-Natal, South Africa.

METHODS

Generalized additive models were used to estimate smoothed HIV incidence rates across partnership age pairings in men and women. Cox proportional hazards regression was used to estimate the relative risk of HIV acquisition by partner age group.

RESULTS

A total of 882 HIV seroconversions were observed in 15 935 person-years for women, incidence rate = 5.5 per 100 person-years [95% confidence interval (CI), 5.2-5.9] and 270 HIV seroconversions were observed in 9372 person-years for men, incidence rate = 2.9 per 100 person-years (95% CI, 2.6-3.2). HIV incidence was highest among 15-24-year-old women reporting partnerships with 30-34-year-old men, incidence rate = 9.7 per 100 person-years (95% CI, 7.2-13.1). Risk of HIV acquisition in women was associated with male partners aged 25-29 years (adjusted hazard ratio; aHR = 1.44, 95% CI, 1.02-2.04) and 30-34 years (aHR = 1.50, 95% CI, 1.08-2.09) relative to male partners aged 35 and above. Risk of HIV acquisition in men was associated with 25-29-year-old (aHR = 1.72, 95% CI, 1.02-2.90) and 30-34-year-old women (aHR = 2.12, 95% CI, 1.03-4.39) compared to partnerships with women aged 15-19 years.

CONCLUSION

Age of sexual partner is a major risk factor for HIV acquisition in both men and women, independent of one's own age. Partner age pairings play a critical role in driving the cycle of HIV transmission.

Age-disparate relationships and HIV incidence in adolescent girls and young women: evidence from Zimbabwe

Supplemental Digital Content is available in the text

Objective:

Age-disparate sexual relationships with older men may drive high rates of HIV acquisition in young women in sub-Saharan Africa, but evidence is limited. We investigate the association between age-disparate relationships and HIV incidence in Manicaland, Zimbabwe.

Design:

A general-population open-cohort study (six surveys) (1998–2013).

Methods:

A total of 3746 young women aged 15–24 years participated in consecutive surveys and were HIV-negative at the beginning of intersurvey periods. Last sexual partner age difference and age-disparate relationships [intergenerational (≥10 years age difference) and intragenerational (5–9 years) versus age-homogeneous (0–4 years)] were tested for associations with HIV incidence in Cox regressions. A proximate determinants framework was used to explore factors possibly explaining variations in the contribution of age-disparate relationships to HIV incidence between populations and over time.

Results:

About 126 HIV infections occurred over 8777 person-years (1.43 per 100 person-years; 95% confidence interval = 1.17–1.68). Sixty-five percent of women reported partner age differences of at least 5 years. Increasing partner age differences were associated with higher HIV incidence [adjusted hazard ratio (aHR) = 1.05 (1.01–1.09)]. Intergenerational relationships tended to increase HIV incidence [aHR = 1.78 (0.96–3.29)] but not intragenerational relationships [aHR = 0.91 (0.47–1.76)]. Secondary education was associated with reductions in intergenerational relationships [adjusted odds ratio (aOR) = 0.49 (0.36–0.68)]. Intergenerational relationships were associated with partners having concurrent relationships [aOR = 2.59 (1.81–3.70)], which tended to increase HIV incidence [aHR = 1.74 (0.96–3.17)]. Associations between age disparity and HIV incidence did not change over time.

Conclusion:

Sexual relationships with older men expose young women to increased risk of HIV acquisition in Manicaland, which did not change over time, even with introduction of antiretroviral therapy.

Age differences between sexual partners, behavioural and demographic correlates, and HIV infection on Likoma Island, Malawi

Patterns of age differences between sexual partners – “age-mixing” – may partially explain the magnitude of HIV epidemics in Sub-Saharan Africa. However, evidence of age-disparity as a risk factor for HIV remains mixed. We used data from a socio-centric study of sexual behaviour in Malawi to quantify the age-mixing pattern and to find associations between relationship characteristics and age differences for 1,922 participants. Three age difference measures were explored as predictors of prevalent HIV infection. We found that for each year increase in male participant age, the average age difference with their partners increased by 0.26 years, while among women it remained approximately constant around 5 years. Women in the study had larger within-individual variation in partner ages compared to men. Spousal partnerships and never using a condom during sex were associated with larger age differences in relationships of both men and women. Men who were more than five years younger than their partners had 5.39 times higher odds (95% CI: 0.93–31.24) of being HIV-infected than men 0–4 years older. The relationship between HIV-infection and age-asymmetry may be more complex than previously described. The role that women play in HIV transmission should not be under-estimated, particularly in populations with large within-individual variation in partner ages.

Individual and Population Level Impact of Key HIV Risk Factors on HIV Incidence Rates in Durban, South Africa

We aimed to estimate the individual and joint impact of age, marital status and diagnosis with sexually transmitted infections (STIs) on HIV acquisition among young women at a population level in Durban, KwaZulu-Natal, South Africa. A total of 3,978 HIV seronegative women were recruited for four biomedical intervention trials from 2002-2009. Point and interval estimates of partial population attributable risk (PAR) were used to quantify the proportion of HIV seroconversions which can be prevented if a combination of risk factors is eliminated from a target population. More than 70% of the observed HIV acquisitions were collectively attributed to the three risk factors: younger age (<25 years old), unmarried and not cohabiting with a stable/regular partner and diagnosis with STIs. Addressing these risks requires targeted structural, behavioural, biomedical and cultural interventions in order to impact on unacceptably high HIV incidence rates among young women and the population as a whole.