Transmission Patterns of HIV and Hepatitis C Virus among Networks of People Who Inject Drugs

The risk-related behaviours and practices associated with injection drug use remain a driver of HIV and hepatitis C virus (HCV) transmission throughout the world. Here we evaluated HIV and HCV transmission patterns in the context of social networks of injection drug users (IDU) recruited from a higher incidence region in order to better understand factors that contribute to ongoing transmission among IDU.IDU recruited through a chain-referral method provided biological specimens for analysis. HIV and HCV positive specimens were sequenced and analyzed using phylogenetic methods (Neighbour-joining and Bayesian) and transmission patterns of HIV and HCV evaluated in the context of the recruitment networks.Among the 407 recruited IDU, HCV and HIV prevalence were 60.6% and 10.1%, respectively; 98% of HIV positive individuals were co-infected with HCV. Thirty-six percent of HCV sequences were associated with clusters, compared to 67% of HIV sequences. Four (16.7%) of the 24 HCV clusters contained membership separated by 2 or fewer recruitment cycles, compared to 10 (41.6%) derived from more than one recruitment component. Two (28.6%) of the 7 HIV clusters contained membership separated by 2 or fewer recruitment cycles while 6 (85.7%) were composed of inter component membership.Few HIV and HCV transmissions coincided with the recruitment networks, suggesting that they occurred in a different social context or a context not captured by the recruitment network. However, among the complete cohort, a higher degree of HIV clustering indicates many are recent infections originating from within current social networks, whereas a larger proportion of HCV infections may have occurred earlier in injecting history and in the context of a different social environment

Networks among injection drug users: Random or scale-free?

The primary goal of this research was to identify whether the structure of the network of individuals who inject drugs and share drug injection equipment in Winnipeg, Canada may be scale-free. Recently, sexual networks have been found to be scale-free in a wide range of populations which has important implications in terms of the spread of disease. Epidemic thresholds do not exist in a scale-free network and as a result even weakly infectious viruses can spread easily through a network of contacts. By analogy, identifying the structure of contacts formed by individuals in other infectious disease networks may also help to define transmission dynamics which can be used to develop more effective interventions. In a series of three papers the scientific literature from a variety of disciplines including physics, epidemiology, mathematical, biological and computer sciences relating to scale free networks is reviewed and integrated; methods used to identify scale-free networks are tested and compared among individuals who inject drugs in Winnipeg, Canada using data from two network studies (a pilot study and a main study); and potential new interventions that could be implemented to help reduce the transmission of HIV and HCV among individuals who inject drugs by the existing needle exchange program are recommended based on the results. Keywords: Scale-free networks, injection drug use, epidemiology, network analysi

HCV genotype distribution.

<p>HCV genotype distribution.</p

Characteristics of recruitment networks.

<p>Characteristics of recruitment networks.</p

Recruitment network #2.

<p>Both <b>A</b> and <b>B</b> represent the same network of 126 participants. Red circles in A indicate HCV positive and orange circles in B indicate HIV positive participants. Coloured boxes indicate phylogenetically related infections within the network. Green frames indicate phylogenetic link(s) to other network(s) with (coloured) or without (white) links within the network. All branches have a length of 1. Vertical scale indicates recruitment rounds (distance) from seed.</p

Composition of Phylogenetic Clusters and links within and between Network Components.

<p>***number of recruitment cycles separating clustered specimens.</p

Phylogenetic analysis.

<p><b>A</b>. Neighbour Joining analysis of all HIV-1 pol sequences generated. <b>B</b>. Analysis of all clustered HCV core sequences. In each tree, bootstrap values greater than 80% are indicated. In situations where HCV clusters based on core analysis (5, 9 & 20) fell below the 80% bootstrap cut off, similar analysis of NS5B (not shown) resolved clusters with bootstrap values above 80%.</p