Theme: Epidemiology & Public Health Research Year: 2017
Background: This study estimated latent classes (i.e., unobserved subgroups in a
population) of people who use drugs in Vancouver, Canada and examined how
these classes relate to phylogenetic clustering of hepatitis C virus (HCV) infection.
Methods: HCV antibody positive people who use drugs from two cohorts in
Vancouver, Canada (1996-2012) with a Core-E2 sequence were included. Timestamped phylogenetic trees were inferred and phylogenetic clustering was
determined by time to most common recent ancestor. Latent classes were estimated
and the association with the phylogenetic clustering outcome assessed using an
inclusive classify/analyse approach.
Results: Among 699 HCV RNA positive participants (26% female, 24% HIV+),
recent drug use included injecting cocaine (80%), injecting heroin (70%), injecting
cocaine/heroin (e.g. speedball, 38%), and crack cocaine smoking (28%). Latent
class analysis identified four distinct subgroups of drug use typologies: 1) cocaine
injecting, 2) opioid and cocaine injecting, 3) crack cocaine smoking, and 4) heroin
injecting and currently receiving opioid substitution therapy (OST). After adjusting for
age and HIV infection, compared to the group defined by heroin injecting and OST,
the odds of phylogenetic cluster membership was greater in the cocaine injecting
group [adjusted OR (aOR): 3.05; 95% CI: 1.76, 5.27] and lower in the crack cocaine
smoking group (aOR: 0.07; 95% CI: 0.01, 0.52).
Conclusions: Identifiable patterns of drug use in this cohort were associated with
close HCV genetic relatedness. Combining latent class and phylogenetic clustering
analyses provides novel insights into the complex dynamics of HCV transmission.
Incorporating differing risk profiles associated with drug use may provide
opportunities to further optimise and target HCV treatment and prevention strategies.
A Disclosure of Interest Statement: Dr Grebely is a consultant/advisor and has
received research grants from Abbvie, Bristol Myers Squibb, Gilead Sciences and
Merck. Prof Montaner has received grants from Abbott, Boehringer-Ingelheim,
Bristol-Myers Squibb, Gilead Sciences, Janssen, Merck and ViiV Healthcare. Prof
Krajden receives research grants from Merck, Gen-Probe (Hologic), Siemens and
Roche. No pharmaceutical grants were received in the development of this study