Quantifying the drivers of HIV transmission and prevention in men who have sex with men: a population model-based analysis in Switzerland. HIV Medicine
Kusejko et al. aimed to identify and quantify the drivers of the HIV epidemic of men who have sex with men (MSM) in Switzerland and to assess the potential impact of interventions to limit transmission.
The authors simulated the HIV epidemic in MSM in Switzerland by stratifying a mathematical model by CD4 count, the care cascade and condom use. The model was parametrised with clinical, epidemiological and behavioural data from the Swiss HIV Cohort Study and surveys in the HIV-negative population.
According to their model, 3.4% of the cases that would otherwise have occurred in 2008–2015 were prevented by early initiation of antiretroviral therapy (ART). Only 0.6% of the cases were attributable to a change in condom use in the HIV-positive population, as less usage is mainly seen in virally suppressed MSM. Most new infections were attributable to transmission from recently infected undiagnosed individuals. It was estimated that doubling the diagnosis rate would have resulted in 11.8% fewer cases in 2001–2015. Moreover, it was estimated that introducing pre-exposure prophylaxis (PrEP) for 50% of those MSM not using condoms with occasional partners would have resulted in 22.6% fewer cases in 2012–2015.
In conclusion, the study found that most new infections are attributable to undiagnosed individuals in the recent phase of the infection and that the ‘test and treat’ strategy hence has the highest impact in reducing the number of new HIV infections. Moreover, protecting individuals who are not using condoms with occasional sexual partners with preexposure prophylaxis (PrEP) was shown to have a major impact even in a short time period. Only a moderate population-level effect was estimated for early initiation of ART and a weak effect for the change in condom use of diagnosed MSM. This very small impact can be explained by the fact that the increase in condomless sex is mainly observed in virally suppressed individuals, that is, individuals who cannot transmit the virus.