Including Online-Recruited Seeds: A Respondent-Driven Sample of Men Who Have Sex With Men.BACKGROUND
 Technology has changed the way men who have sex with men (MSM) seek sex and socialize, which may impact the implementation of respondent-driven sampling (RDS) among this population.  Initial participants (also known as seeds) are a critical consideration in RDS because they begin the recruitment chains.  However, little information is available on how the online-recruited seeds may effect RDS implementation.


 OBJECTIVE
 The objectives of this study were to compare (1) online-recruited versus offline-recruited seeds and (2) subsequent recruitment chains of online-recruited versus offline-recruited seeds.


 Between 2012 and 2014, we recruited MSM using RDS in Vancouver, Canada.  RDS weights were used with logistic regression to address each objective.


 A total of 119 seeds were used, 85 of whom were online-recruited seeds, to recruit an additional 600 MSM.  Compared with offline-recruited seeds, online-recruited seeds were less likely to be HIV-positive (OR 0.34, 95% CI 0.13-0.88), to have attended a gay community group (AOR 0.33, 95% CI 0.12-0.90), and to feel gay community involvement was "very important" (AOR 0.16, 95% CI 0.03-0.93).  Online-recruited seeds were more likely to ask a sexual partner's HIV status always versus <50% of the time (AOR 5.21, 95% CI 1.17-23.23), to have watched the Pride parade (AOR 6.30, 95% CI 1.69-23.45), and to have sought sex online (AOR 4.29, 95% CI 1.53-12-12.05).  Further, compared with recruitment chains started by offline-recruited seeds, recruits from chains started by online-recruited seeds (283/600, 47.2%) were less likely to be HIV-positive (AOR 0.25, 95% CI 0.16-0.40), to report "versatile" versus "bottom" sexual position preference (AOR 0.56, 95% CI 0.35-0.88), and to be in a relationship lasting >1 year (AOR 1.65, 95% CI 1.06-2.56).  Recruits of online seeds were more likely to be out as gay for longer (eg, 11-21 vs 1-4 years, AOR 2.22, 95% CI 1.27-3.88) and have fewer Facebook friends (eg, 201-500 vs >500, AOR 1.69, 95% CI 1.02-2.80).


 CONCLUSIONS
 Online-recruited seeds were more prevalent, recruited fewer participants, but were different from those recruited offline.  This may therefore help create a more diverse overall sample.  Our work has shown the value of geosocial networking apps for aiding RDS recruitment efforts, especially when faced with slow participation uptake by other means.  Understanding the degree to which networks interact will be an important next step in confirming the efficacy of online RDS recruitment strategies.
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