Reinfection with hepatitis C virus (HCV), after undergoing successful treatment for the liver infection, can occur following a subsequent sexual exposure to the virus, according new data involving eight gay and bisexual HIV-positive men reported today at the 15th Conference on Retroviruses and Opportunistic Infections (CROI) in Boston.

Evidence confirming that HCV can be spread sexually continues to mount, with the vast majority of reports involving men who have sex with men. There’s also no shortage of research confirming that individuals who successfully undergo a year of toxic antiviral treatment for HCV are not always in the clear—some patients see a relapse of their infection, whereas others can be reinfected with another strain of HCV via the same transmission route responsible for their first infection with the virus.

Rachel Jones, MD, of the Chelsea and Westminster NHS Foundation Trust in London, and her colleagues set out to determine whether infection relapse or reinfection was to blame for a resurgence of detectable HCV viral loads in a small group of HIV-positive gay and bisexual men, several months after being successfully treated for the hepatitis C.

The researchers first queried databases at both Chelsea and Westminster and Royal Free Hospitals to find individuals with detectable HCV viral loads following a sustained virologic response (SVR) to initial hepatitis C treatment. An SVR is typically defined as an undetectable HCV viral load for at least six months after spontaneously clearing the infection or following completion of standard treatment: pegylated interferon plus ribavirin.

Once the individuals were found, the genes from their HCV samples—collected during the first and second period of detectable virus—were compared. Sexually transmitted infection diagnoses during the HCV SVR—a potential marker of sexual behavior that may have facilitated a transmission of a second hepatitis C virus—were also recorded in the database.

Of the 211 HIV/HCV-coinfected individuals in the data, 16 had at least two episodes of HCV infection, with the second episode typically diagnosed following a routine liver function test. All were men who have sex with men. They had been infected with HIV for approximately four years and, on average, were 38 years old when they were diagnosed with the initial HCV infection. The average length of the SVR, between periods of detectable HCV, was 20 months.

Dr. Jones’s group was able to collect paired samples from eight of the individuals. Genetic analysis revealed two individuals with viruses that were similar enough to indicate late relapse. In the remaining six, there were enough differences between the paired viruses to indicate reinfection with different strains.

All but two individuals had at least one sexually transmitted infection during their SVR periods, syphilis being the most common.

In conclusion, Dr. Jones and her colleagues suggest that six of the men were likely reinfected with HCV after successfully completing treatment for an initial infection. These reinfections, the authors said, were likely related to ongoing high-risk sexual activity. In the other two patients, the strains were closely related, likely indicative of a late relapse of the infection—or possibly reinfection from a common source.