|Epidemiology; HIV; Loss to follow up; Men who have sex with men; Respondent drive sampling; Risk reduction counselling and testing
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Background: Respondent-driven-sampling (RDS) has been recognized as a method for sampling from most hard-to-reach populations. Meanwhile, loss to follow up of the participants in follow up studies usually reduces the validity of the association measured in observational studies, and this problem cannot be overcame through data analysis.Methods: In a cross sectional study in Nanjing city of Jiangsu province of China, 430 MSM were recruited including 9 seeds in 14 weeks of study period using RDS. Information regarding socio-demographic characteristics and sexual risk behavior were collected and testing was done for HIV and syphilis. Duration, completion, participant characteristics and the equilibrium of key factors were used for assessing feasibility of RDS. All the HIV negative participants were followed up at 6, 12 and 18 months to evaluate behavioral changes after counseling to reduce risk behaviors. Logistic regression was performed to identify the factors correlated with loss to follow up.Results: In the study sample, adjusted HIV and syphilis prevalence were 6.6% and 14.6% respectively, whereas HIV incidence was 5.2 per 100 person-years. The incidence was 3.8 during six to 12 months, and 1.1 during 12 to 18 months. Although there was a tendency for recruitment within the same self-identified group, considerable cross-group recruitment was also seen. During the study period, the reported unprotected anal intercourse (UAI) significantly decreased from 60.9% to 42.9%. The proportion of participants who had one or no partner significantly increased from 40.9% to 48.0%. The study also found that some risk behaviors decreased between baseline and 12 months, followed by a slight increase between 12 and 18 months. In addition, loss to follow up for the MSM study in Nanjing was associated with younger age, small social network, lower education, and non-official residence in Jiangsu.Conclusion: RDS was found to be a potential efficient and feasible sampling method for recruiting a diverse sample of MSM in a reasonable time. Reductions in UAI can be achieved through counseling and testing, but may wane over time. The factors correlated with loss-to-follow-up found in of our study may be helpful to increase the retention rate of future cohort studies.