Social and Behavioral Factors Associated with HCV Transmission in Injection Drug Users

Since hepatitis C virus (HCV) infection can spread through sharing of contaminated syringes and other injection equipment, the disease is "hyperendemic" among injection drug users, with an annual HCV incidence rate of about 10%-40%. However, the social and behavioral factors underlying transmission in this population are not well understood.

As reported in the September 15, 2006 Journal of Infectious Diseases, researchers conducted a case-control study of HCV seroconversion in drug injectors in Washington State, focusing on transmission within networks. Case subjects with new HCV infections (n = 17) and HCV negative control subjects (n = 42) reported information about their drug injection and sex partners, and referred up to 5 partners for interviews and blood testing.

Results

78% of recent drug injection partnerships involved behavior that could transmit HCV.

HCV positive case subjects and HCV negative control subjects had similar demographic characteristics and reported similar behaviors.

However, the newly infected case subjects had more HCV-infected injection partners and consequently engaged in high-risk injection risk behavior with more infected partners.

The network of people who injected drugs together was mostly connected, dense, and cyclic, while the drug injectors' sexual network was highly fragmented.

Although participants generally injected with partners of a similar age, most HCV negative study participants had recently injected with infected partners.

In at least 1 of 4 pairs of genetically linked HCV infections, transmission appeared to be due to sharing injection equipment other than syringes.

Except for transmission pairs, network distance between incident case subjects and genetic distance between their HCV variants were uncorrelated.

In conclusion, the researchers wrote, "Without dramatic reductions in injection risk behaviors, shattering of cohesive injection networks, and/or broad coverage of an effective vaccine, HCV will likely remain hyperendemic in drug injectors."

Discussion

In their discussion, the authors noted that nearly 25% of reported injection partnerships involved syringe sharing, while nearly 80% involved some type of injection behavior that could transmit HCV. Given that the injectors' sexual network was highly fragmented, they suggested it would be "unable to serve as a scaffold for sustained transmission by itself," in the absence of risky injection activity.

"Because case subjects and control subjects were similar in their injection risk behavior with their partners overall," they wrote, "seroconversion was mostly an accident of network position -- that is, injecting with more individuals who happened to be HCV infected."

Given the frequent turnover in injection partners, they added, "we expect most HCV-uninfected injection drug users will eventually be in similar positions in the injection network and subsequently [will] acquire HCV."

09/26/06

Reference
D D Brewer, H Hagan, and D G Sullivan. Social structural and behavioral underpinnings of hyperendemic hepatitis C virus transmission in drug injectors. Journal of Infectious Diseases 194(6): 764-772. September 15, 2006.