Young women in
Zimbabwe have an especially high risk of infection with HIV if they have a
sexual partner who is ten or more years older, investigators report in the
online edition of AIDS. Such inter-generational
relationships increased the risk of contracting HIV by approximately 75%.
“We found that
age-disparate sexual relationships are associated with increased HIV incidence
among young women aged 15-24 years, particularly where partners are ten or more
years older,” comment the authors. “Although only a minority of young women
reported partners ten or more years older, the proportion was still substantial
(21%)…so these inter-generational relationships are likely to be an important
contributor to new infections in young women and to the HIV epidemic in this
setting.”
The investigators
call for the roll-out of interventions, including pre-exposure prophylaxis (PrEP), to reduce the HIV risk
for young women in relationships with significantly older men.
Young women in
sub-Saharan Africa have very high rates of HIV infection. In Zimbabwe, incidence
of HIV among women aged 15-24 years is twice as high as that observed in men of
the same age group.
Modelling studies
have shown that sexual relationships with older men – or age-disparate
relationships – could be a major reason why young women have such high HIV
incidence rates. This is because HIV prevalence is higher among older men than
younger men, meaning that young women in relationships with older men are more
likely to be exposed to HIV.
However, the
precise impact of age-disparate relationships on HIV risk is not fully
understood.
An international
team of investigators therefore examined data collected between 1998 and 2013
in eastern Zimbabwe to see if having an older male sexual partner was
associated with an increased risk of infection with HIV for women aged between
15 and 24 years.
Women included in
the study were HIV-negative at baseline and completed at least two follow-up
visits. At each visit, social and economic data were collected and if sexually
active, participants were asked about the age of their most recent sexual
partner.
Relationships were
categorised as age-homogenous if there was a 0-4 years difference;
intra-generational if the difference was between 5-9 years; and
inter-generational if the partner was at least 10 years older.
The investigators
performed a set of analyses to see if age and other social, economic and sexual
risk factors were associated with an increased risk of HIV incidence.
A total of 3082
women met the inclusion criteria and contributed 3746 study visits. There were
126 new HIV infections during 8777 person-years of follow-up, a rate of 1.43
per 100 person-years.
In all, 2262 study
visits involved women who reported sexual activity, and 1734 of these yielded
data on the age of the most recent sexual partner.
Just over a fifth
of women (21%) had a partner who was ten or more years older and 45% had a
partner who was 5-9 years older. These proportions remained steady during the
study. HIV prevalence in men declined over time, but remained constantly higher
among men aged 30 years and older.
Age difference was
associated with higher HIV incidence among younger women. Each one-year
difference in age increased the risk by 5% (aHR = 1.05 per year; 95% CI,
1.01-1.09).
Incidence was
higher in inter-generational relationships (2.56 per 100 person-years) compared
to age-homogeneous relationships (1.49 per 100 person-years).
Similar patterns
were found when the investigators took into account factors such as area of
residence (urban, peri-urban, rural), household income, wealth and orphanhood.
Women with a
secondary education were significantly less likely to report an
inter-generational relationship compared to women with lower levels of
education (aOR = 0.49; 95% CI, 0.36-0.68).
An inter-generational
sexual relationship was associated with the older male having a concurrent sexual
partner (aOR = 2.59; 95% CI, 1.81-3.70), and there was a trend for this to be
associated with higher HIV incidence among young women (aHR = 1.74; 95% CI,
0.96-3.17).
The association
between inter-generational relationships did not change as antiretrovirals were
rolled out across Zimbabwe.
“As far as we are
aware, this is the first study to demonstrate an association between increasing
partner age and HIV incidence in a representative general-population sample
covering pre- and post-ART [antiretroviral therapy] periods,” note the authors. “The results from this
study provide evidence that age-disparate relationships can be an important
contributor to the continued high HIV incidence rates in adolescent girls and
young women in sub-Saharan African populations.”