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HIV most often passed on by younger gay men who have undiagnosed HIV, are not on treatment, and have an ongoing partnership
Roger Pebody, 2014-12-11 10:20:00
A modelling study based on the UK’s HIV epidemic among gay
men estimates that two-thirds of infections originate in men with undiagnosed
HIV, 85% in men who are not taking treatment and 90% within the context of an
ongoing sexual partnership. Moreover, HIV transmissions most frequently involve
men under the age of 35 who report relatively high levels of sexual activity,
according to the study published online ahead of print in AIDS.
But the findings suggest that men with primary infection
contribute less to onward transmission than is sometimes thought.
The model aimed to simulate the underlying drivers of the
epidemic – the contribution of various behavioural and biological factors to
HIV transmission between men who have sex with men (MSM).
A better understanding of who is passing HIV on could help
with the design and targeting of HIV prevention and testing interventions. It
could also help explain why – despite the high uptake of HIV treatment – there
are no signs of a fall in new HIV infections among gay men in the UK.
The researchers fed into their model data on HIV diagnoses,
uptake of HIV treatment, CD4 counts, the sexual behaviour of UK gay men (condom
use, rate of partner change, serosorting, etc.), as well as the risk of HIV
transmission during various sexual behaviours and at various viral loads.
The key figures produced are known to statisticians as
‘population attributable fractions’ – this estimates the proportion of HIV
transmissions that originate in a particular group of people. For example, the
method can estimate the proportion of transmissions that come from people with
diagnosed and undiagnosed HIV infection. As there is some fuzziness in some (but
not all) of these estimations, the researchers also report a range of credible
figures – the true figure is likely to be somewhere between the two.