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Introduction: China is amidst a sexual revolution, with changing sexual practices and behaviors. Sex–seeking mobile phone applications (gay apps) that allow multiple people to meet up quickly may facilitate group sex. This study was therefore undertaken to evaluate group sex among Chinese MSM and to better understand factors associated with group sex. Methods: An online survey was conducted from September-October 2014, collecting data on socio-demographics, sexual behaviors, use of gay apps and occurrence of group sex among Chinese MSM. Univariate and multivariable logistic regressions were used to compare group sex and non-group sex participants. Results: Of the 1,424 MSM, the majority were under 30 years old (77.5%), unmarried (83.9%), and were gay apps users (57.9%). Overall, 141 (9.9%) participants engaged in group sex in the last 12 months. Multivariate analyses showed that men living with HIV, engaged in condomless anal intercourse with men, and used gay apps were more likely to engage in group sex, with adjusted ORs of 3.74 (95% CI 1.92–7.28), 2.88 (95% CI 2.00–4.16) and 1.46 (95% CI: 1.00–2.13), respectively. Among gay app users, the likelihood of group sex increases with the number of sex partners and the number of sex acts with partners met through a gay app. Conclusions: Chinese MSM who engage in group sex are also more likely to engage in other risky sexual behaviors, and gay app use may facilitate group sex. Further research is needed among MSM who engage in group sex in order to target interventions and surveillance. [ABSTRACT FROM AUTHOR]

The HIV-1 epidemic among men who have sex with men (MSM) has been spreading throughout China. Shanghai, a central gathering place for MSM, is facing a continuously increasing incidence of HIV-1 infection. In order to better understand the dynamics of HIV-1 diversity and its influence on patient’s immune status at baseline on diagnosis, 1265 newly HIV-1-infected MSM collected from January 2009 to December 2013 in Shanghai were retrospectively analyzed for genetic subtyping, CD4+T cell counts, and viral loads. HIV-1 phylogenetic analysis revealed a broad viral diversity including CRF01_AE (62.13%), CRF07_BC (24.51%), subtype B (8.06%), CRF55_01B (3.24%), CER67_01B (0.95%), CRF68_01B (0.4%), CRF08_BC (0.08%) and CRF59_01B (0.08%). Twenty-four unique recombination forms (URFs) (1.98%) were identified as well. Bayesian inference analysis indicated that the introduction of CRF01_AE strain (1997) was earlier than CRF07_BC strain (2001) into MSM population in Shanghai based on the time of the most recent common ancestor (tMRCA). Three epidemic clusters and five sub-clusters were found in CRF01_AE. Significantly lower CD4+T cell count was found in individuals infected with CRF01_AE than in those infected with CRF07_BC infection (P<0.01), whereas viral load was significantly higher those infected with CRF01_AE than with CRF07_BC (P<0.01). In addition, the patients with >45 years of age were found to have lower CD4+T cell counts and higher viral loads than the patients with <25 years of age (P<0.05). This study reveals the presence of HIV-1 subtype diversity in Shanghai and its remarkable influence on clinical outcome. A real-time surveillance of HIV-1 viral diversity and phylodynamics of epidemic cluster, patient’s baseline CD4+T cell count and viral load would be of great value to monitoring of disease progression, intervention for transmission, improvement of antiretroviral therapy strategy and design of vaccines. [ABSTRACT FROM AUTHOR]