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Objectives: Understanding the drivers of HIV‐1 transmission is of importance for curbing the ongoing epidemic. Phylogenetic methods based on single viral sequences allow us to assess whether two individuals are part of the same viral outbreak, but cannot on their own assess who potentially transmitted the virus. We developed and assessed a molecular epidemiology method with the main aim to screen cohort studies for and to characterize individuals who are 'potential HIV‐1 transmitters', in order to understand the drivers of HIV‐1 transmission. Methods: We developed and validated a molecular epidemiology approach using longitudinally sampled viral Sanger sequences to characterize potential HIV‐1 transmitters in the Swiss HIV Cohort Study. Results: Our method was able to identify 279 potential HIV‐1 transmitters and allowed us to determine the main epidemiological and virological drivers of transmission. We found that the directionality of transmission was consistent with infection times for 72.9% of 85 potential HIV‐1 transmissions with accurate infection date estimates. Being a potential HIV‐1 transmitter was associated with risk factors including viral load [adjusted odds ratiomultivariable (95% confidence interval): 1.86 (1.49–2.32)], syphilis coinfection [1.52 (1.06–2.19)], and recreational drug use [1.45 (1.06–1.98)]. By contrast for the potential HIV‐1 recipients, this association was weaker or even absent [1.18 (0.82–1.72), 0.89 (0.52–1.55) and 1.53 (0.98–2.39), respectively], indicating that inferred directionality of transmission is useful at the population level. Conclusions: Our results indicate that longitudinally sampled Sanger sequences do not provide sufficient information to identify transmitters with high certainty at the individual level, but that they allow the drivers of transmission at the population level to be characterized. [ABSTRACT FROM AUTHOR]

Objectives: Chemsex refers to the use of sex‐enhancing drugs among men who have sex with men (MSM) in combination with specific sexual and social behaviours. Longitudinal data on this development and the associated health risks are scarce. Methods: Data on all recreational drugs reported in the Swiss HIV Cohort Study (SHCS) from 2007 to 2017 were collected. Drug use was analysed longitudinally for all drug classes. In addition, potential associations between patient characteristics and the consumption of methamphetamine, γ‐hydroxybutric acid/γ‐butyrolactone (GHB/GBL), 3,4‐methylenedioxymethamphetamine (MDMA/XTC), cocaine and amphetamine were analysed. Results: We analysed 166 167 follow‐up entries for 12 527 SHCS participants, including 7101 free text field entries containing information about recreational drugs other than cannabis, cocaine and heroin. Overall, we observed a stable percentage (9.0%) of recreational drug use (excluding cannabis, amyl nitrite and prescription drugs). For MSM, however, there was an increase in overall drug use from 8.8% in 2007 to 13.8% in 2017, with particularly large increases for methamphetamine (from 0.2 to 2.4%; P < 0.001) and GHB/GBL (from 1.0 to 3.4%; P < 0.001). The use of each of the potentially sex‐enhancing drugs methamphetamine, GHB/GBL, cocaine, XTC/MDMA and amphetamine was significantly associated with condomless sex with nonsteady partners, and higher prevalences of depression, syphilis and hepatitis C. Conclusions: The significant increase in the use of chemsex drugs among MSM in the SHCS and the strong association with coinfections and depression highlights the need for harm reduction programmes tailored to MSM. According to our results, improving knowledge about recreational drugs is important for all health care professionals working with people living with HIV. [ABSTRACT FROM AUTHOR]

Objectives: Despite the huge success of antiretroviral therapy (ART), there is an ongoing HIV epidemic among men who have sex with men (MSM) in resource‐rich countries. Understanding the driving factors underlying this process is important for curbing the epidemic. Methods: We 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. Results: According to our model, 3.4% of the cases that would otherwise have occurred in 2008–2015 were prevented by early initiation of 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. Conclusions: By combining observational data on the relevant epidemiological and clinical processes with a mathematical model, we showed that the 'test and treat' approach is most effective in reducing the number of new cases. 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. Protecting HIV‐negative individuals who are not using condoms with PrEP was shown to have a major impact. [ABSTRACT FROM AUTHOR]

Objectives Here we examined the hypothesis that some stable HIV-infected partnerships can be found in cohort studies, as the patients frequently attend the clinic visits together. Methods Using mathematical approximations and shuffling to derive the probabilities of sharing a given number of visits by chance, we identified and validated couples that may represent either transmission pairs or serosorting couples in a stable relationship. Results We analysed 434 432 visits for 16 139 Swiss HIV Cohort Study patients from 1990 to 2014. For 89 pairs, the number of shared visits exceeded the number expected. Of these, 33 transmission pairs were confirmed on the basis of three criteria: an extensive phylogenetic tree, a self-reported steady HIV-positive partnership, and risk group affiliation. Notably, 12 of the validated transmission pairs (36%; 12 of 33) were of a mixed ethnicity with a large median age gap [17.5 years; interquartile range ( IQR) 11.8−22 years] and these patients harboured HIV-1 of predominantly non-B subtypes, suggesting imported infections. Conclusions In the context of the surge in research interest in HIV transmission pairs, this simple method widens the horizons of research on within-pair quasi-species exchange, transmitted drug resistance and viral recombination at the biological level and targeted prevention at the public health level. [ABSTRACT FROM AUTHOR]