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CATIE News - Social networks and HCV transmission

2011 Feb 22 - Transmission of hepatitis C virus (HCV) is occurring in Canada and other high-income countries, mostly through sharing contaminated equipment for substance use. Additionally, sexual transmission of HCV has been documented in men who have sex with men (MSM) through unprotected anal sex and other activities.

As symptoms of HCV infection may be mild and because they tend to often resemble symptoms of a flu-like illness, acute HCV infection may go unnoticed.

HCV attacks the liver and slowly damages this organ so that eventually serious complications, liver failure, liver cancer and death can occur. In people co-infected with HIV and HCV, the course of liver damage is accelerated, as HIV infection weakens the immune system. Although HCV treatment is available it is not always effective in cases of co-infection and can cause unpleasant side effects.

A research team conducted the Australian Trial in Acute Hepatitis C (ATAHC), which was designed to closely monitor a group of HIV-negative and HIV-positive people who developed acute HCV infection. The findings from this study suggest that HCV is not occurring in isolated cases. Rather, the researchers found that infections are occurring in groups or clusters of MSM who appear to be socially connected. These social networks seem to be based on sexual orientation rather than specific high-risk behaviours (injecting drugs or unprotected anal sex). Seeking, interacting with and focusing on these social networks may be useful for studying the spread of HCV and for helping to prevent the further spread of this infection and perhaps others, including HIV and other sexually transmitted infections (STIs).

Study details

The research team recruited participants from clinics across Australia who had acute HCV infection. Participants were interviewed and had blood drawn for analysis. They also completed self-administered questionnaires about risk behaviours. Blood samples were collected and later analysed for HCV's genetic material (RNA). This RNA was investigated and assessed to help classify HCV into its subtypes (also called genotypes) and to see how closely HCV in each person was related to HCV in other people in the study.

The basic profile of 163 participants in the study was as follows:

  • 72% men, 28% women
  • age - 34 years
  • 31% were co-infected with HIV
  • 41% had symptoms of a flu-like infection after they were infected with HCV
  • 76% were injection drug users (IDUs)
  • 16% were currently depressed
  • 10% were taking methadone or buprenorphine


The study team found that the most common mode of HCV infection was sharing equipment for injecting drugs-this was responsible for 73% of infections. Most of the remaining infections were spread via sex between MSM.

Results-Sexual transmission of HCV among women

Four cases of acute HCV infection occurred in HIV-negative women who did not inject drugs. All four women had male sexual partners who were known to be positive for HCV. Unfortunately, researchers did not publish detailed information about the sexual practices of these women but concluded that HCV was likely transmitted via unprotected intercourse with their HCV-positive partners. Further research is required with heterosexual women, both HIV positive and negative, to assess their risk for acquiring HCV infection during unprotected anal and vaginal sex.

Results-Sexual transmission of HCV among men

Among 25 men who were infected with HCV via sex, the majority (23 men, or 92%) were also HIV positive and were infected by having unprotected sex with other men.

As for the two remaining HIV-negative men who were infected sexually, one was infected with HCV during sex with another man and the other was infected with HCV during sex with a woman known to be HCV positive.


Through extensive investigation, researchers were able to classify most study participants into three groups, depending on their HIV status and mode of HCV infection, as follows:

  • HIV-negative IDUs (96 people)
  • HIV-positive IDUs (23 people)
  • HIV-positive HCV sexual acquisition group (23 people)

HCV-Genotypes and relations

Technicians analysed HCV from participants and found that most had either genotype 1a or 3a. They also assessed HCV cases for their relatedness or similarity.

Among HIV-negative people, only 8% had HCV that was closely related to HCV found in other HIV-negative people in the study.

Among people who were HIV positive, 51% had HCV that was closely related to HCV found in other HIV-positive people in this study. A group of people with closely related HCV is called a cluster.

The clusters in this Australian study contained HIV-positive people, some of whom injected drugs and others who did not. The researchers said that this finding suggests that "social networks exist in groups of HIV-positive MSM that contain IDUs and non-IDUs."

Previous research has found that substance use that does not involve needles (eg. inhaling drugs via straws) seems to play a role in facilitating sexual transmission of HCV infection. Based on this previous research as well as the interviews in the present study, the Australian researchers suggested that it is "highly likely that social mixing of HIV-infected individuals with all types of drug-using behaviours is occurring and fuelling the ongoing [HCV] epidemic." Furthermore, the absence of any HIV-negative heterosexual IDUs in the study's clusters suggests that these "networks of HCV transmissions are predominantly defined by sexual orientation rather than risk behaviour."

Based on the Australian findings, it may be useful for researchers to conduct field work in order to study sexual and social networks that focus on sexual orientation so that educational and disease prevention programs can be strengthened.

Related findings in the U.S.

American researchers recently conducted a study to assess new cases of HCV transmission among HIV-positive men. In the American study of 1,839 men, at least 36 developed HCV infection. In 75% of these cases of HCV infection, the men did not inject drugs, and so transmission was likely through unprotected anal sex. The American researchers cite recent studies with MSM in Australia and Switzerland in which factors such as unprotected anal sex and co-infection with syphilis likely played a role in HCV transmission.

What is noteworthy about the American study is that many of the participants were taking highly active antiretroviral therapy (HAART) and those who had recent HCV infection were also likely to have HIV viral load that was greater than 400 copies/ml in their blood. The researchers said that there are at least two possible reasons for this association between raised HIV viral loads and acute HCV infection. First, perhaps engagement in high-risk activities, including substance use, may cause some people to forget to take HAART exactly as directed, and so their HIV viral load rises. Second, because HCV infects the liver, this organ temporarily becomes dysfunctional as it reacts to the acute infection and becomes inflamed. The liver processes many medicines, particularly those for the treatment of HIV infection. If this organ is temporarily inflamed, the concentration of these medicines can build up in the body, causing toxicity and side effects. This may cause some affected people to temporarily stop taking HAART, and so HIV viral load rises.

Future studies of HCV transmission

The American researchers noted that future studies of acute HCV should consider detailed investigations with participants to assess behaviours such as sero-sorting (people having unprotected sex with people of the same HIV serostatus). Some researchers have suggested that sero-sorting among HIV-positive men might explain the rise in HCV co-infection in this population. The study team suggested several other areas for investigation for possible roles in HCV transmission, including the role of non-injected substance use (such as crystal methamphetamine) and "the reuse of condoms, gloves and sex toys during traumatic sex practices."

The American team also noted that both the European AIDS Clinical Society and the New York State Department of Health AIDS Institute recommend annual testing for HCV infection for HIV-positive patients. Such testing could help uncover previously unknown cases of HCV co-infection and provide an opportunity for doctors and nurses to help educate patients about HCV transmission, care and treatment.

-Sean R. Hosein


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  2. Ghosn J, Deveau C, Goujard C, et al. Increase in hepatitis C virus incidence in HIV-1-infected patients followed up since primary infection. Sexually Transmitted Infections . 2006 Dec;82(6):458-60.
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  7. Zablotska IB, Imrie J, Prestage G, et al. Gay men's current practice of HIV seroconcordant unprotected anal intercourse: serosorting or seroguessing? AIDS Care . 2009 Apr;21(4):501-10.
  8. van de Laar MJ. HIV/AIDS and other STIs in men who have sex with men-a continuous challenge for public health. Eurosurveillance. 2009 Nov 26;14(47). pii: 19423.

From Canadian AIDS Treatment Information Exchange (CATIE). For more information visit CATIE's Information Network at


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