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Risk score accurately predicts which pregnant and postpartum women would benefit most from PrEP
Michael Carter, 2017-01-10 07:00:00
A risk score based
on routine assessments carried out during antenatal care in resource-limited
settings can accurately predict which pregnant and breastfeeding women have an
especially high risk of infection with HIV and would therefore benefit from
pre-exposure prophylaxis, investigators report in the online edition of Clinical Infectious Diseases.
infection with HIV included a partner of unknown HIV status, number of lifetime
sexual partners, syphilis, bacterial vaginosis and vaginal candidiasis. A
composite risk score higher than six was associated with a six-fold increase in
HIV incidence; the score was a more accurate predictor of HIV infection than
any individual risk factor. Women with risk scores above six accounted for only
16% of the cohort but 56% of HIV infections.
The study involved
over 1300 pregnant women in Kenya.
“We found that a
composite risk score including male partner, behavioral and clinical
characteristics have good predictive ability to identify women most likely to
acquire HIV,” write the authors. “Our analysis contributes a unique risk
assessment of an important subpopulation and is the first, to our
knowledge, that assesses HIV risk during pregnancy and postpartum, a period of
high HIV incidence and PrEP implementation opportunities.”
Nearly 80% of all
HIV infections involving younger women occur in sub-Saharan Africa and
there is a high HIV incidence among younger women and men in this setting.
Pregnancy is a
period of biological changes that can increase susceptibility to HIV. It is also
a time of behavioural changes – such as reduced condom use – that can increase
the risk of exposure to HIV. A systematic review involving over 22,000 African
women found HIV incidence rates during pregnancy and postpartum of 3.8 and
4.7/100 person-years, respectively. These rates compare to those observed in
high-risk populations such as female sex workers.
have been used to identify subgroups most at risk of HIV, including
men-who-have-sex-with-men, HIV-serodiscordant African couples and young
(non-pregnant) African women. However, no tool has been used to identify which
pregnant and postpartum women have an especially high risk of infection with
such a tool could help identify which women would most benefit from PrEP and
help minimise unnecessary use of the therapy.
the Mama Salama Study therefore used data from a longitudinal cohort of 1304
pregnant and postpartum women in Kenya to develop a risk score capable of
identifying individuals with the greatest risk of infection with HIV during
these periods of increased susceptibility.
The study was
conducted between 2011 and 2014. Pregnant females aged 14 years and older who
were HIV-negative at baseline were eligible for recruitment. Participants were
followed for nine months postpartum.
At each follow-up
visit, participants were tested for HIV. Questionnaires were also administered
on sociodemographic factors, reproductive history, contraception and condom
use, medical history and genital symptoms. Patients were also screened for
bacterial vaginosis and vaginal thrush.
Data were gathered
on incident HIV infections and the authors identified factors associated with
this outcome. They used this data to develop risk scores predictive of
infection with HIV.
randomised into two groups: one to develop the risk score (derivation cohort),
the other to test the score’s robustness (validation cohort).
patients contributed 1235 person-years of follow-up during which there were 25
incident HIV infections (incidence rate 2.31 per 100 person-years).
The median age was
22 years. Three-quarters of women were married. Only 7% reported a history of
sexually transmitted infections, 55% reported sex without a condom in the
previous month and 29% had a partner of unknown HIV status.
There were 14
incident infections in the derivation cohort, a rate of 2.31 per 100 person
years. Increased risk of acquisition of HIV was associated with relationship
duration of less than one year, having a male partner of unknown HIV status, lifetime
number of sexual partners, syphilis, bacterial vaginosis and vaginal thrush.
Characteristics with the highest risk scores were syphilis and having a partner
of unknown HIV status.
HIV incidence was
13.6 per 100 person-years among women with a risk score above eight compared to
an incidence of 0.9 per 100 person-years for women with a risk score below
A simplified risk
score was developed based on assessments routinely available in antenatal care
setting. Bacterial vaginosis and vaginal thrush were therefore excluded. HIV
incidence was 9 per 100 person-years among women with a risk score above six,
compared to 1.0 per 100 person-years for women with a lower risk score. This
simplified risk score correctly identified 64% of women who acquired HIV in the
derivation cohort; only 16% of women had a risk score above six.
The risk score similarly
predicted HIV risk in the validation cohort.
In the overall
cohort, women with a risk score above eight had a six-fold increase in their
risk of infection with HIV (HR 6.19; 95% CI 2.78-13.78, p < 0.001), with
each one-point increment associated with a 1.3-fold increase in HIV risk. The
simplified risk score of six was associated with a five-fold increase in HIV
risk (HR 5.12; 95% CI 2.33-11.2, p < 0.001). Once again, each one-point
increment was associated with a 1.3 fold increase in risk. The simplified score
of six predicted 56% of HIV infections and 16% of women had a risk score at
“We found a
combination of characteristics routinely assessed during antenatal care,
yielded high predictive utility for HIV risk in pregnant and postpartum women,”
conclude the authors. “Targeting PrEP for women at high risk of HIV acquisition
could have substantial impact on maternal and infant HIV incidence, limit
unnecessary PrEP exposure to women at low risk, and use resources efficiently.”