HIV Superinfection Not Seen in Amsterdam Gay Men 
By Liz Highleyman

Over the course of the AIDS epidemic public officials have cautioned that HIV positive people should avoid unprotected sex with each other in order to prevent “superinfection,” or infection with additional viral strains that could potentially be more aggressive or drug-resistant. Some advocates, however, promote “serosorting” as a responsible risk-reduction strategy for HIV positive gay men.

Several prior studies have failed to find evidence of superinfection, or indicate that it happens only rarely — around 50 cases total — typically during the early years after infection with the initial virus.

As described in the June 2011 Journal of Infectious Diseases, Andrea Rachinger from the University of Amsterdam and colleagues looked for evidence of superinfection over time among participants in the Amsterdam Cohort Studies on HIV Infection and AIDS.

The researchers analyzed HIV-1 C2-C4 envelope (env) and gag sequences generated from longitudinal blood samples from 15 gay/bisexual men who had not yet started antiretroviral therapy. Serum samples had been collected around the time of self-reported risk for HIV sexual transmission, including unprotected anal sex or having other sexually transmitted infections.

The study authors used maximum likelihood phylogenetic analysis to detect evidence of new HIV strains in a total of 124 serum samples. They looked at a median of 8 samples per participant with a median follow-up period of 5.8 person-years, or about 88 total person-years.

Phylogenetic analysis of a total of 907 C2-C4 env sequences and 672 gag sequences revealed no case of HIV superinfection, yielding a superinfection incidence rate of 0 per 100 person-years.

Based on these findings, the authors wrote, “We conclude that HIV-1 superinfection incidence is low in this subgroup of homosexual men who reported unsafe sexual behavior.”

However, they suggested, “Additional studies are required to estimate the impact of also other factors, which may determine the risk to acquire HIV-1 superinfection.”

Investigator affiliations: Department of Experimental Immunology, Sanquin Research, Landsteiner Laboratory, and Center for Infection and Immunity Amsterdam (CINIMA) at the Academic Medical Center of the University of Amsterdam; Cluster of Infectious Diseases, Department of Research, Health Service of Amsterdam; Department of Internal Medicine, CINIMA, Academic Medical Center of the University of Amsterdam, Amsterdam, Netherlands.

Reference
A Rachinger, P Manyenga, JA Burger, et al. Low Incidence of HIV-1 Superinfection Even After Episodes of Unsafe Sexual Behavior of Homosexual Men in the Amsterdam Cohort Studies on HIV Infection and AIDS. Journal of Infectious Diseases 203(11):1621-1628 (abstract). June 2011

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