For the study, which was published in the peer-reviewed open access journal PLoS ONE, the investigators examined how ART use, unprotected sex and HIV testing impacted HIV trends in UK MSM over the past 30 years. Using data routinely collected from the UK (“surveillance data”), data on self-reported condom use among MSM, and other information, the researchers built complex computer models to simulate sexual risk behaviour, HIV transmission, HIV progression (the wellness extent to which the infection has damaged the immune system) and the effect of ART in MSM on HIV incidence in the UK from 1980-2010.
Amongst other assumptions, the researchers assumed that all transmissions took place through unsafe (condomless) sex, and that after HIV diagnosis a proportion of men substantially reduce unsafe sex with short-term partners, and the model suggested that after high HIV incidence in the early 1980s, there was indeed this decline in sexual risk behaviour and a resulting reduction in HIV incidence. However, they also discovered that if ART had never been introduced, HIV incidence would be 68% higher that it is now.
This led them to draw the conclusion that the net increase in incidence of HIV in the UK has occurred because ART has partially removed the fear of MSM to have sex without a condom. As a result, the researchers said that increased condom use should be encouraged. They also said that more HIV testing could reduce the rates of the disease further, noting that randomised controlled trials (RCTs) are yet to reliably assess the balance of the benefits and risks of starting ART soon after diagnosis. However, the researchers did allow that trials are ongoing.