title: Hepatitis C virus phylogenetic clustering is associated with the social-injecting network in a cohort of people who inject drugs.
abstract: It is hypothesized that social networks facilitate transmission of the hepatitis C virus (HCV). We tested for association between HCV phylogeny and reported injecting relationships using longitudinal data from a social network design study. People who inject drugs were recruited from street drug markets in Melbourne, Australia. Interviews and blood tests took place three monthly (during 2005-2008), with participants asked to nominate up to five injecting partners at each interview. The HCV core region of individual isolates was then sequenced and phylogenetic trees were constructed. Genetic clusters were identified using bootstrapping (cut-off: 70%). An adjusted Jaccard similarity coefficient was used to measure the association between the reported injecting relationships and relationships defined by clustering in the phylogenetic analysis (statistical significance assessed using the quadratic assignment procedure). 402 participants consented to participate; 244 HCV infections were observed in 238 individuals. 26 genetic clusters were identified, with 2-7 infections per cluster. Newly acquired infection (AOR = 2.03, 95% CI: 1.04-3.96, p = 0.037, and HCV genotype 3 (vs. genotype 1, AOR = 2.72, 95% CI: 1.48-4.99) were independent predictors of being in a cluster. 54% of participants whose infections were part of a cluster in the phylogenetic analysis reported injecting with at least one other participant in that cluster during the study. Overall, 16% of participants who were infected at study entry and 40% of participants with newly acquired infections had molecular evidence of related infections with at least one injecting partner. Likely transmission clusters identified in phylogenetic analysis correlated with reported injecting relationships (adjusted Jaccard coefficient: 0.300; p<0.001). This is the first study to show that HCV phylogeny is associated with the injecting network, highlighting the importance of the injecting network in HCV transmission.
authors.affiliation: Centre for Population Health, Burnet Institute, Melbourne, Victoria, Australia. rachelsd@burnet.edu.au
authors.forename: Rachel
authors.initials: R
authors.lastname: Sacks-Davis
authors.forename: Galina
authors.initials: G
authors.lastname: Daraganova
authors.forename: Campbell
authors.initials: C
authors.lastname: Aitken
authors.forename: Peter
authors.initials: P
authors.lastname: Higgs
authors.forename: Lilly
authors.initials: L
authors.lastname: Tracy
authors.forename: Scott
authors.initials: S
authors.lastname: Bowden
authors.forename: Rebecca
authors.initials: R
authors.lastname: Jenkinson
authors.forename: David
authors.initials: D
authors.lastname: Rolls
authors.forename: Philippa
authors.initials: P
authors.lastname: Pattison
authors.forename: Garry
authors.initials: G
authors.lastname: Robins
authors.forename: Jason
authors.initials: J
authors.lastname: Grebely
authors.forename: Alyssa
authors.initials: A
authors.lastname: Barry
authors.forename: Margaret
authors.initials: M
authors.lastname: Hellard
mesh_terms: D000328:Adult; D005260:Female; D005838:Genotype; D016174:Hepacivirus / Q000145:classification / Q000235:genetics*; D006526:Hepatitis C / Q000635:transmission; D006801:Humans; D008297:Male; D010802:Phylogeny; D012307:Risk Factors; D015819:Substance Abuse, Intravenous / Q000821:virology*; D055815:Young Adult