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Networking strategy may decrease HCV prevalence among injection drug users
In a new study, researchers in Australia found that using a social network-based approach to treating injection drug users with hepatitis C virus infection led to decreased hepatitis C virus prevalence and increased efficacy of treatment over time.
“Though it is unrealistic to assume that we can observe all of the network of an [injection drug user], we suggest that HCV infection is highly likely to arise from an injector’s network, even if not from the observed network,” the researchers wrote.
Researchers enrolled a cohort of injection drug users in Melbourne, Australia, between 2005 and 2007 to determine how a person’s social network can affect HCV transmission. Using the snowball sampling method, 258 nodes from 258 participants were included and represented 524 injection drug users overall, according to the research.
To test their theory on a larger population, researchers generated 100 networks with 20 subnetworks, which contained 524 injection drug users each, using the “fixed-node number and Pnet’s standard Metroplois-hastings [Markov chain Monte Carlo]” model for the final analysis.
Information on each patients’ social networks, drug injection behavior and blood samples were evaluated during a follow-up of 5 years. An exponential random graph model was used to calculate the number of contacts and how often drugs were injected, to conclude if these factors impacted time to diagnosis of HCV.
Five treatment strategies were investigated by the researchers: treat the infected node with the highest degree first; treat the infected node with the greatest number of uninfected node neighbors; treat the infected node with the lowest number of infected node neighbors; treat randomly selected nodes; and treat your friends.
Results showed that as treatment coverage increased, HCV prevalence decreased.
“The drop in prevalence is most marked with higher efficacy moving from coverage of 5 to 15 [injection drug users] per 1,000 per year,” the researchers wrote.
All five treatment strategies showed better results compared with no treatment at all, and the treat your friends strategy had the highest treatment efficacy rates.
“For examples, at 10 years, treating 25 per 1,000 [injection drug users], the prevalence drops from 50% to 40% for the random strategy and to 33% for the treat your friends strategy (6.5% difference; 95% CI, 5.1-8.1),” the researchers wrote.
“The structure of [injection drug users’] injecting network influences HCV transmission and impacts significantly on the effectiveness of treatment strategies,” the researchers concluded. “As well as benefiting individual [injection drug users] by reducing their risk of HCV reinfection, taking [injection drug users’] networks into account will ensure that new HCV treatments produce maximum community benefit by reducing the prevalence of HCV among [injection drug users].”
Disclosure: The researchers report no relevant financial disclosures.
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The efficacy of antiviral therapy for chronic hepatitis C infection has improved rapidly with the emergence of new direct-acting antiviral regimens. The large-scale impact associated with this trend is anticipated to become more pronounced as successful eradication of the virus may significantly decrease the prevalence of cirrhosis and liver-related deaths associated with hepatitis C infection. However, challenges remain in the effort to achieve early detection, targeting high-risk populations, and selection of treatment candidates. As a larger proportion of individuals are successfully treated, a major consideration involves efforts to minimize transmission within groups at the highest risk of exposure.
Injection drug use is currently the most common source of acute exposure to the hepatitis C virus, accounting for at least one-half of new acute symptomatic infections in the US as reported through population-based surveillance programs. Several studies involving high-risk populations have described an increasing prevalence of hepatitis C with duration of drug use, with reports of greater than 70% seropositivity within 3 to 5 years of exposure to injection drugs and a prevalence of over 90% in some populations. Treatment of injection drug users remains controversial, particularly in light of the potential for re-infection.
In a recent study by Hellard and colleagues, a cohort of injection drug users was observed in order to define their social networking characteristics, including patterns of injection drug use contact between individuals. Characteristics of this network were then simulated in models in order to test various treatment strategies within this population. A treatment strategy based on identifying an infected person and then treating them as well as their immediate contacts with infection led to the highest potential for achieving a decline in prevalence over a 10 year period. The investigators note that prior attempts at modeling hepatitis C exposure assume homogeneous mixing within the population; however, a greater understanding of behavioral patterns within these specific groups may provide critical insight that may guide successful treatment strategies. Although more investigation will be required to further define this concept, efforts to minimize the prevalence of hepatitis C within these high-risk populations may be the key to achieving a major decline in the overall prevalence of chronic hepatitis C in the future.