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Abstract
Respondent-driven sampling (RDS) is a form of link-tracing sampling, a sampling technique used for "hard-to-reach" populations that aims to leverage individuals' social relationships to reach potential participants. There is a growing interest in the estimation of uncertainty for RDS as recent findings suggest that most variance estimators underestimate variability. Recently, Baraff et al. proposed the tree bootstrap method based on resampling the RDS recruitment tree, and empirically showed that this method outperforms current bootstrap methods. However, some findings suggest that the tree bootstrap (severely) overestimates uncertainty. In this article, we propose the neighborhood bootstrap method for quantifying uncertainty in RDS. We prove the consistency of our method under some conditions and investigate its finite sample performance, through a simulation study, under realistic RDS sampling assumptions.

This is the final published version of an article published in the Open Access Journal BMC Public Health. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/) ; Researchers and activists have long called for changes to blood donation policies to end what is frequently framed as unjustified bans or deferral periods for men who have sex with men (MSM). Since 2016, in Canada, a man had to be abstinent from all sexual contact (anal or oral sex) with other men for at least 12 months in order to be an eligible blood donor. As of June 3, 2019, this deferral period was reduced to 3 months. Methods: To better understand the acceptance of existing deferral policies and possible future policy, we conducted 47 in-depth interviews with a demographically diverse sample of gay, bisexual, queer, and other men who have sex with men (GBM) in Canada's three largest cities: Vancouver, (n = 17), Toronto (n = 15), and Montreal (n = 15). Interviews were coded in NVivo 11 following an inductive thematic analysis. We focus on men's preferred policy directions and their opinions about a policy change proposed by Canada's blood operators: a 3-month deferral for all sexual activity between men. We interviewed GBM approximately one-year before this new deferral policy was approved by Health Canada. Results: Most participants were opposed to any deferral period in relation to MSM-specific sexual activity. A fair and safe policy was one that was the "same for everyone" and included screening for several risk factors during the blood donation process with no categorical exclusion of all sexually active MSM. Participants believed that multiple "gender blind" and HIV testing-related strategies could be integrated into the blood donation process. These preferences for a move away from MSM-specific exclusions aligned with their opinions concerning the possible change to a 3-month MSM deferral, for which participants shared three overarching perspectives: (1) step in the right direction; (2) ambivalence and uncertainty; and (3) not an improvement. Conclusion: A predominant assertion was that a change from a 12-month to a 3-month deferral period would not resolve the fundamental issues of fairness and equity affecting blood screening practices for GBM in Canada. Many participants believed that blood donation policy should be based on more up-to-date scientific evidence concerning risk factor assessment and HIV testing. ; This research received funding support from the Canadian Blood Services MSM Research Grant Program, funded by the federal government (Health Canada) and the provincial and territorial ministries of health. The larger Engage study is funded by the Canadian Institutes of Health Research (#TE2–138299), the Canadian Association for HIV/AIDS Research (#Engage), the Ontario HIV Treatment Network (#1051), and Ryerson University. DG is supported by a Canada Research Chair in Sexual and Gender Minority Health. NJL is supported by a Scholar Award from the Michael Smith Foundation for Health Research (#16863). DJB and TAH are supported by OHTN Applied Research Chairs.

AbstractIntroductionTreatment as prevention strategies have been variously applied across provinces in Canada. We estimated HIV care cascade indicators and correlates of unsuppressed viral load (VL) among gay, bisexual and other men who have sex with men (GBM) recruited in Vancouver, Toronto and Montreal.MethodsSexually active GBM, aged ≥16 years, were recruited through respondent‐driven sampling (RDS) from February 2017 to August 2019. Participants completed a Computer‐Assisted Self‐Interview and tests for HIV and other sexually transmitted infections (STIs). We conducted bivariate analyses comparing RDS‐adjusted proportions across cities. We used multivariable logistic regression to examine factors associated with having a measured VL ≥ 200 copies/mL with data pooled from all three cities.ResultsWe recruited 1179 participants in Montreal, 517 in Toronto and 753 in Vancouver. The RDS‐adjusted HIV prevalence was 14.2% (95% CI 11.1 to 17.2) in Montreal, 22.1% (95% CI 12.4 to 31.8) in Toronto and 20.4% (95% CI 14.5 to 26.3) in Vancouver (p < 0.001). Of participants with confirmed HIV infection, 3.3% were previously undiagnosed in Montreal, 3.2% undiagnosed in Toronto and 0.2% in Vancouver (p = 0.154). In Montreal, 87.6% of GBM living with HIV were receiving antiretroviral therapy (ART) and 10.6% had an unsuppressed VL; in Toronto, 82.6% were receiving ART and 4.0% were unsuppressed; in Vancouver, 88.5% were receiving ART and 2.6 % were unsuppressed (p < 0.001 and 0.009 respectively). Multivariable modelling demonstrated that participants in Vancouver (adjusted odds ratio [AOR]=0.23; 95% CI 0.06 to 0.82), but not Toronto (AOR = 0.27; 95% CI 0.07 to 1.03), had lower odds of unsuppressed VL, compared to Montreal, as did older participants (AOR 0.93 per year; 95% CI 0.89 to 0.97), those at high‐risk for hazardous drinking (AOR = 0.19; 95% CI 0.05 to 0.70), those with a primary care provider (AOR = 0.11; 95% CI 0.02 to 0.57), and those ever diagnosed with other STIs (AOR = 0.12; 95% CI 0.04 to 0.32).ConclusionsGBM living in Montreal, Toronto and Vancouver are highly engaged in HIV testing and treatment and all three cities have largely achieved the 90‐90‐90 targets for GBM. Nevertheless, we identified disparities which can be used to identify GBM who may require additional interventions, in particular younger men and those who are without a regular primary care provider.

AbstractIntroductionAccessibility of pre‐exposure prophylaxis (PrEP) in Canada remains complex as publicly funded coverage and delivery differs by province. In January 2018, PrEP became publicly funded and free of charge in British Columbia (BC), whereas PrEP coverage in Ontario and Montreal is more limited and may require out‐of‐pocket costs. We examined differences over time in PrEP uptake and assessed factors associated with PrEP awareness and use.MethodsGay, bisexual and other men who have sex with men (GBM) were recruited through respondent‐driven sampling (RDS) in Toronto, Vancouver and Montreal, Canada, in a prospective biobehavioural cohort study. We applied generalized estimating equations with hierarchical data (RDS chain, participant, visit) to examine temporal trends of PrEP use and correlates of PrEP awareness and use from 2017 to 2020 among self‐reported HIV‐negative/unknown GBM.ResultsOf 2008 self‐identified HIV‐negative/unknown GBM at baseline, 5093 study visits were completed from February 2017 to March 2020. At baseline, overall PrEP awareness was 88% and overall PrEP use was 22.5%. During our study period, we found PrEP use increased in all cities (all p<0.001): Montreal 14.2% during the first time period to 39.3% during the last time period (p<0.001), Toronto 21.4–31.4% (p<0.001) and Vancouver 21.7–59.5% (p<0.001). Across the study period, more Vancouver GBM used PrEP than Montreal GBM (aOR = 2.05, 95% CI = 1.60–2.63), with no significant difference between Toronto and Montreal GBM (aOR = 0.90, 95% CI = 0.68–1.18).ConclusionsFull free‐of‐charge public funding for PrEP in BC likely contributed to differences in PrEP awareness and use. Increasing public funding for PrEP will improve accessibility and uptake among GBM most at risk of HIV.