Social and structural factors associated with substance use within the support network of adults living in precarious housing in a socially marginalized neighborhood of Vancouver, Canada

BackgroundThe structure of a social network as well as peer behaviours are thought to affect personal substance use. Where substance use may create health risks, understanding the contribution of social networks to substance use may be valuable for the design and implementation of harm reduction or other interventions. We examined the social support network of people living in precarious housing in a socially marginalized neighborhood of Vancouver, and analysed associations between social network structure, personal substance use, and supporters’ substance use.MethodsAn ongoing, longitudinal study recruited 246 participants from four single room occupancy hotels, with 201 providing social network information aligned with a 6-month observation period. Use of tobacco, alcohol, cannabis, cocaine (crack and powder), methamphetamine, and heroin was recorded at monthly visits. Ego- and graph-level measures were calculated; the dispersion and prevalence of substances in the network was described. Logistic mixed effects models were used to estimate the association between ego substance use and peer substance use. Permutation analysis was done to test for randomness of substance use dispersion on the social network.ResultsThe network topology corresponded to residence (Hotel) with two clusters differing in demographic characteristics (Cluster 1 –Hotel A: 94% of members, Cluster 2 –Hotel B: 95% of members). Dispersion of substance use across the network demonstrated differences according to network topology and specific substance. Methamphetamine use (overall 12%) was almost entirely limited to Cluster 1, and absent from Cluster 2. Different patterns were observed for other substances. Overall, ego substance use did not differ over the six-month period of observation. Ego heroin, cannabis, or crack cocaine use was associated with alter use of the same substances. Ego methamphetamine, powder cocaine, or alcohol use was not associated with alter use, with the exception for methamphetamine in a densely using part of the network. For alters using multiple substances, cannabis use was associated with lower ego heroin use, and lower ego crack cocaine use. Permutation analysis also provided evidence that dispersion of substance use, and the association between ego and alter use was not random for all substances.ConclusionsIn a socially marginalized neighborhood, social network topology was strongly influenced by residence, and in turn was associated with type(s) of substance use. Associations between personal use and supporter’s use of a substance differed across substances. These complex associations may merit consideration in the design of interventions to reduce risk and harms associated with substance use in people living in precarious housing.

一、研究背景
社交网络结构与同伴行为均被学界认为会对个体的物质使用行为产生影响。鉴于物质使用行为会带来健康风险，解析社交网络对物质使用的影响机制，可为减害干预或其他相关干预措施的设计与实施提供参考价值。本研究针对温哥华某社会边缘化社区中的不稳定住房居住人群，对其社会支持网络展开调研，并分析了社交网络结构、个体物质使用行为与支持对象物质使用行为之间的关联。

二、研究方法
本项持续纵向研究从4家单人出租旅馆（single room occupancy hotels，SRO）中招募了246名参与者，其中201名参与者提供了符合6个月观察周期的社交网络相关信息。研究人员在每月随访中记录了参与者的烟草、酒精、大麻、可卡因（快克与粉剂）、甲基苯丙胺及海洛因使用情况。计算了自我中心网络与整体网络层面的各项指标，并对网络内物质使用的分散程度与流行率进行了描述。采用逻辑混合效应模型，估算个体物质使用行为与同伴物质使用行为之间的关联。通过置换检验分析社交网络中物质使用分散模式的随机性。

三、研究结果
网络拓扑结构与居住场所高度对应，形成两个人口统计学特征存在显著差异的聚类群组：群组1（旅馆A，占比94%的成员）、群组2（旅馆B，占比95%的成员）。网络内物质使用的分散模式因网络拓扑结构与物质类型的不同而存在差异。甲基苯丙胺使用整体发生率为12%，几乎仅局限于群组1，群组2中未发现此类使用行为。其余物质的使用模式则各不相同。整体而言，在6个月的观察周期内，个体的物质使用行为未出现显著变化。个体的海洛因、大麻或快克可卡因使用行为，与同伴的同类物质使用行为存在显著关联。个体的甲基苯丙胺、粉剂可卡因或酒精使用行为，则未与同伴的同类使用行为呈现显著关联，仅在网络中物质使用密集区域内，甲基苯丙胺使用存在例外关联。对于存在多种物质使用行为的同伴而言，其大麻使用行为与个体更低的海洛因使用量、更低的快克可卡因使用量相关。置换检验结果显示，并非所有物质的使用分散模式以及个体与同伴使用行为间的关联均呈现随机性。

四、研究结论
在社会边缘化社区中，社交网络拓扑结构受居住场所的影响极强，并反过来与物质使用类型密切相关。个体与支持对象间的物质使用关联模式因物质类型不同而存在差异。此类复杂关联可为针对不稳定住房居住人群的物质使用相关风险与危害的干预措施设计提供重要参考依据。