A study that looked at the way risk of HIV transmission changed over time in a group of gay men during a six- to eight-year period has found that there was vast variation in the degree of risk men subjected themselves to, the length of time they were at risk and, as a result, HIV incidence.
The researchers analysed the number of times cohort members took sexual risks over the study period (by allocating a “risk score” to each six-month period) and found that men’s risk scores tended to be consistent, and to fall into three different groups. It found that one-in-seven men belonged to a very high risk group, a third of whom became infected with HIV over the study period. Just under a quarter belonged to a moderate risk group, of whom 10% became HIV positive.
The other two-thirds were at low risk of HIV, except for short periods; 3% of them acquired HIV. Being in the one-third of the cohort that did take more risks was associated with being white, having a high income, and being younger; in addition, being in the most at-risk one-seventh of the group was associated with depression and taking recreational drugs.
The authors specifically did this cohort analysis because they wanted better information that could help in the targeting of pre-exposure prophylaxis (PrEP) at the right groups: one of the reasons this prevention method has taken off slowly in the US and not yet received approval elsewhere is concern about its cost. Cost-effectiveness studies suggest that PrEP will only be economical if taken by people with the highest risk of HIV infection (see this report for one example).
It is, however, of broader interest, as the first-ever study to demonstrate a relationship between specific characteristics and what the authors call “risk trajectories” – longitudinal patterns of risk over time.
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To read the study abstract, click here.