Search

Background: Uncertainty surrounds why hepatitis C virus (HCV) is concentrated among HIV-positive men who have sex with men (MSM). We used mathematical modelling to explore reasons for these infection patterns, and implications for HCV treatment-as-prevention.Methods: Using a joint MSM HIV/HCV transmission model parameterized with UK behavioural data, we considered how biological (heightened HCV infectivity and reduced spontaneous clearance among HIV-positive MSM) and/or behavioural factors (preferential sexual mixing by HIV status and risk heterogeneity) could concentrate HCV infection in HIV-positive MSM as commonly observed (5-20 times the HCV prevalence in HIV-negative MSM; defined as the HCV ratio). We explored how HCV treatment-as-prevention impact varies under differing HCV ratios.Results: Biological factors produced low HCV ratios (< 3), not explaining the skewed epidemic. However, combining preferential mixing by HIV status with sexual risk behaviour heterogeneity produced high HCV ratios (> 10) that were highly sensitive to both factors. Irrespective of the HCV ratio or behavioural/biological factors, HCV treatment of HIV-diagnosed MSM markedly reduced the HCV prevalence among HIV-positive MSM, but less impact was achieved among all MSM for lower HCV ratios.Conclusions: Sexual behaviour patterns likely drive observed HCV infection patterns among HIV-positive MSM. Changes in these patterns could disseminate HCV amongst HIV-negative MSM, limiting the impact of targeting HCV treatment to HIV-diagnosed MSM. [ABSTRACT FROM AUTHOR]

Background There is controversy about what sexual practices or secretions (e.g. saliva) transmit Neisseria gonorrhoeae in men who have sex with men (MSM). To date, no studies have modelled potential transmission when one sexual practice follows another in the same sexual encounter or the role of sexual secretions in transmission. Methods We developed eight compartmental models to examine three additional transmission routes: (1) oral sex followed by anal sex (or vice versa); (2) using saliva as a lubricant for penile-anal sex, and (3) oral sex followed by oral-anal sex (rimming) or vice versa. For comparison, we used a baseline model that did not include any of these three transmission routes. The seven other models added one of the additional transmission routes or combinations of the three of them to the baseline model. Results The baseline model could replicate infection at the single anatomical site but underestimated infection at more than one anatomical site ('multi-site infection'). When we added the three transmission routes to the baseline model, oral sex followed by anal sex or vice versa could replicate the prevalence of multi-site infection. The other two transmission routes alone or together could not replicate multi-site infection without the inclusion of oral sex followed by anal sex. Conclusions Our model suggests sexual practices that involve oral followed by anal sex (or vice versa) may be important for explaining the high proportion of multi-site infection. Key messages For Neisseria gonorrhoeae transmission, additional transmission routes are necessary to replicate multi-site infection. [ABSTRACT FROM AUTHOR]

Background Despite the continuing decline of HIV/AIDS incidence and prevalence in the general population of Vietnam, HIV rates remains high in three key subpopulations: injecting drug users (IDUs), men who have sex with men (MSM) and female sex workers (FSWs). This study aims to identify the common sociodemographic characteristics and behavioural risk factors among three key populations for HIV infection in Vietnam. Methods This study used a systematic review and meta-analysis to synthesise findings from published studies on HIV prevalence and associated risk factors among the three at-risk groups. Five electronic databases were used to identify peer-reviewed articles in relevant topics. Comprehensive Meta-Analysis software was used to estimate pooled prevalence in the combined study population and to determine the effect sizes of the common risk factors on HIV outcome. Results Of the 18 included studies, 6 focused on IDUs, 8 on FSWs and 4 on MSM, accounting for a total of 16,304 participants. The overall prevalence of HIV among the three at-risk groups based on meta-analysis was 11.8% (95%CI: 0.072-0.188). The identified common risk behaviours for HIV infection included injecting drug use (OR: 21.3, 95%CI: 6.5-69.3), sharing injecting equipment (OR: 4.2, 95%CI: 2.1-8.2) and inconsistent condom use (OR: 2.6, 95%CI: 1.5-4.4). The associated socio-demographic characteristics with HIV (+) included young age, single/ unmarried, low education and income. Conclusions/Key messages The findings of this study suggested that injecting drug use may can contribute to developing more affective prevention measures targeting these high-risk groups and reducing the risk of HIV transmission to the general population. [ABSTRACT FROM AUTHOR]

Background To monitor the prevalence of HIV and syphilis as well as behaviours, a sentinel site for men who have sex with men was established in Harbin in 2002. With additional funding, the sentinel surveillance evolved into annual cross-sectional surveys since 2006.Methods Behavioural and serological data collected in five consecutive cross-sectional surveys were analysed. SPSS 13.0 was applied to compare prevalence of HIV and syphilis as well as behavioural variables over time by demographic variables, bivariate and multivariate analysis.Results The prevalence of HIV and syphilis increased from 1.0% in 2006 to 7.5% in 2010 and from 9.2% in 2006 to 22.4% in 2009, respectively, whereas the rate of unprotected anal intercourse decreased from 61.3% in 2006 to 47.1% in 2010. Syphilis positivity and HIV infection are independently associated with each other across years. The rate of unprotected anal sex remains high although it has decreased over the years.Conclusion Findings support an increasing prevalence of HIV and syphilis among men who have sex with men in Harbin. Targeted behavioural intervention and syphilis treatment are urgently needed to prevent the epidemic from growing. [ABSTRACT FROM AUTHOR]

Background: Hard-to-reach population subgroups are typically investigated using convenience sampling, which may give biased estimates. Combining information from such surveys, a probability survey and clinic surveillance, can potentially minimize the bias. We developed a methodology to estimate the prevalence of undiagnosed HIV infection among men who have sex with men (MSM) in England and Wales aged 16-44 years in 2003, making fuller use of the available data than earlier work.Methods: We performed a synthesis of three data sources: genitourinary medicine clinic surveillance (11 380 tests), a venue-based convenience survey including anonymous HIV testing (3702 MSM) and a general population sexual behaviour survey (134 MSM). A logistic regression model to predict undiagnosed infection was fitted to the convenience survey data and then applied to the MSMs in the population survey to estimate the prevalence of undiagnosed infection in the general MSM population. This estimate was corrected for selection biases in the convenience survey using clinic surveillance data. A sensitivity analysis addressed uncertainty in our assumptions.Results: The estimated prevalence of undiagnosed HIV in MSM was 2.4% [95% confidence interval (95% CI 1.7-3.0%)], and between 1.6% (95% CI 1.1-2.0%) and 3.3% (95% CI 2.4-4.1%) depending on assumptions; corresponding to 5500 (3390-7180), 3610 (2180-4740) and 7570 (4790-9840) men, and undiagnosed fractions of 33, 24 and 40%, respectively.Conclusions: Our estimates are consistent with earlier work that did not make full use of data sources. Reconciling data from multiple sources, including probability-, clinic- and venue-based convenience samples can reduce bias in estimates. This methodology could be applied in other settings to take full advantage of multiple imperfect data sources. [ABSTRACT FROM AUTHOR]

Background Chlamydia trachomatis (CT) and Mycoplasma genitalium (MG) are two common sexually transmitted infections in men who have sex with men that are assumed to be transmitted only by oral and anal sex. However, this assumption has not been tested in mathematical models before. Methods To test a variety of potential transmission routes against the known proportion of infections at the oropharynx, mouth and anus, we established 20 compartmental models involving different sexual practices. We tested transmission by a) only anal sex and oral sex; b) adding rimming and kissing to anal and oral sex, and c) adding sequential sexual practices (e.g. oral sex followed by oral-anal sex (rimming) or vice versa. Results We could not replicate the proportion of anatomical sites infected with CT using anal or oral sex alone or by adding riming and kissing. However, if we included sequential sexual practices, then we were able to replicate the prevalence of CT at each site including infection at more than one site. In contrast, we were able to replicate infection for MG at the three sites using transmission routes that involved only anal sex and oral sex without the need for adding any other routes of transmission. Conclusions Our model indicates that more complicated transmission routes are required to explain the observed prevalence of infection with CT, but that for MG transmission involving only anal and oral sex is sufficient. Key messages Unlike CT, MG transmission does not require more complicated transmission routes. [ABSTRACT FROM AUTHOR]