Sex and drug use driving HCV epidemic among HIV-positive gay men in Australia; other study shows small epidemic in US

The hepatitis C epidemic in HIV-positive gay men is being driven by both sexual transmission and injecting drug use, Australian research published in the online edition of Clinical Infectious Diseases suggests. Sexual risk and injecting drug use were reported by HIV-positive gay men newly diagnosed with the virus.

Phylogenetic analysis showed that 51% of infections in gay men could be placed within transmission clusters. No heterosexual injecting drug users were identified in the transmission clusters that involved gay men, suggesting to the investigators that “these networks of HCV [hepatitis C virus transmission] are predominately defined by sexual orientation rather than risk behaviour.”

There were few cases of sexual transmission of hepatitis C in HIV-negative individuals, and in every instance the individual had a partner who was known to be infected with hepatitis C.

Separate US research conducted at HIV treatment centres across the country showed that there is a low incidence of hepatitis C in HIV-positive men. However, 75% of all new diagnoses appeared to be related to sexual risk factors rather than injecting drug use.

Acute hepatitis C in Australia

Investigators from the Australia Trial of Acute Hepatitis C (ATAHC) wished to establish if the epidemics of hepatitis C in injecting users and HIV-positive gay men overlapped. They also wished to see if there was any evidence of sexual transmission of the virus in HIV-negative individuals.

A total of 163 patients who had recently been infected with hepatitis C were recruited to the study, 29% of whom were HIV-positive.

Injecting drug use was identified as the route of hepatitis C transmission in 73% of patients, sexual transmission in 18%, and other (such as medical transmission or assault), in 9% of cases.

Of the 29 cases of sexual transmission, four involved women who had a male partner who was known to be hepatitis C-infected.

Only two of the men who acquired hepatitis C sexually were HIV-negative. One believed he was infected by a woman, and the other reported sex with another man.

All 23 HIV-infected individuals who acquired hepatitis C were gay men.

The investigators constructed a phylogenetic tree using samples taken from 112 patients. This enabled them to identify four distinct transmission clusters. Only 8% of HIV-negative individuals could be placed within a transmission network. This involved a pair of female HIV-negative injecting drug users.

However, 51% of infections in gay men could be placed in transmission networks.

The only HIV-negative gay men who was infected with hepatitis C was in a cluster with two HIV-positive gay men who injected drugs.

“These findings further extend the debate on the role of sexual and IDU-related transmission of HCV in HIV-infected and HIV-uninfected MSM populations and have implications for appropriate targeting of future public health messages,” comment the investigators.

Incident hepatitis C among HIV-positive men in the US

In a separate study US investigators examined rates of incident hepatitis C infections among HIV-positive men between 1996 and 2008.

Earlier studies have shown have identified outbreaks of sexually transmitted hepatitis C in New York and California. The researchers wished to see if there was evidence of an epidemic elsewhere in the US.

A total of 1830 men who were clear of hepatitis C at baseline and who had at least one subsequent antibody test were included in the study. At the time of the first test 94% of individuals were taking HIV therapy, and only 6% reported current or prior injecting drug use.

There were 36 hepatitis C infections, and this provided an incidence of 0.51 cases per 100 person years. Only 25% of individuals newly infected with hepatitis C had any history of injecting drug use. The investigators believe that sexual transmission is the most likely explanation for the other infections.

“At-risk HIV-infected persons should have access to ongoing HCV surveillance,” conclude the investigators.