A man who
is in a relationship with an HIV-positive woman has a three times higher risk
of acquiring HIV if his partner also has bacterial vaginosis, Craig Cohen told
the Sixth International AIDS Society conference (IAS 2011) in Rome today. Whereas it has been previously
established that bacterial vaginosis increases a woman’s risk of acquiring HIV,
this is the first time that it has been shown to increase her risk of
transmission to sexual partners.
vaginosis (BV) is a condition which occurs when the normal balance of bacteria
in the vagina becomes disrupted. This can result in an over-growth of certain
bacteria (flora), which may be accompanied by symptoms such as discharge, itching and
pain. It can sometimes cause pelvic
inflammatory disease and lead to problems with fertility and childbirth.
A number of
prospective studies have established that having BV is associated – for women –
with an increased risk of acquiring HIV. Studies on men’s risk of acquiring HIV
when their sexual partners have bacterial vaginosis have not previously been
some studies have shown that BV is associated with an increase of HIV viral
load in the genital tract. There is also evidence that HIV-positive women who
have bacterial vaginosis when they give birth are at greater risk of passing
HIV on to their child.
presented an analysis of data on couples recruited to the Partners in
Prevention study, conducted in seven countries of southern and eastern Africa. There were 2236 HIV-negative men in the cohort
who had an HIV-positive female partner. Both partners were followed for up to
been together for a median of five years and three-quarters were married. A
third reported having unprotected sex, although condoms and counselling were
provided by the researchers. The HIV-positive partner had to have a CD4 cell
count above 250 cells/mm3 and not be on HIV treatment at the start
of the study.
10,000 study visits at which vaginal flora was assessed, 34.9% of women had
bacterial vaginosis, 22.8% had intermediate flora and 42.8% had normal flora.
course of the study, 57 of the men became HIV positive when HIV genotyping (env
and gag) could confirm that they had similar virus to that of their partner. In
other words, they probably hadn’t acquired HIV outside the primary
investigators then identified the measurement of vaginal flora for their
partner that was taken closest to the estimated date of seroconversion (no more
than three months previously). This data was missing for seven women, leaving
50 couples in the analysis.
transmissions originated from women with normal flora, ten from women with
intermediate flora and 31 from women with bacterial vaginosis.
controlling for a large number of potentially confounding factors
(sociodemographic, behavioural and biological), men whose partners had BV had a
three times higher risk of acquiring HIV than other men (hazard ratio 3.06,
95% confidence interval 1.35 – 6.95).
BV did have higher genital viral loads (3.23 log, compared to 3.04 log in women
with normal flora). This was statistically significant, but Cohen suggested
that it probably isn’t clinically significant.
two other hypotheses that could explain the increased risk to male partners.
Firstly, that normal bacteria may be virucidial against HIV, reducing the
proportion of virus that is infectious. Secondly, that bacterial vaginosis
could indirectly increase the male partner’s susceptibility to HIV. Cohen noted
that long-term sexual partners share genital flora, with men acquiring bacteria
from their partners. It is possible, he suggested, that bacteria may activate
Langerhans cells and CD4+ T-cells, making the man more susceptible to HIV
A significant challenge in acting on this research is that current treatment strategies for bacterial vaginosis are inadequate, with low cure rates and the problem often recurring.