Study finds no evidence of HIV superinfection among highly exposed couples

A study of 33 HIV-positive couples who engage in frequent unprotected sex finds no evidence of HIV superinfection, the term given to the idea that one can be infected with multiple strains of HIV that are slightly genetically different. The study by researchers at the Gladstone Institute of Virology and Immunology in San Francisco, which was presented Thursday at the 15th International AIDS Conference in Bangkok, Thailand, calls into question the widely held perception that HIV-positive people are susceptible to additional infections by viral variants that may be drug-resistant or more virulent, says lead researcher Robert Grant, MD. The ongoing investigation, known as the Positive Partners study, began in 2001 and will eventually involve up to 200 HIV-infected couples. It is designed to investigate the incidence of HIV superinfection. In addition to the couples cited in these preliminary study findings, 30 individuals reporting multiple partners were included in the study. One of them, a participant who had recently developed HIV infection, presented with a highly divergent variation of the virus at a follow-up visit. "This one case demonstrates that people who have recently developed HIV-1 can harbor multiple viruses," notes Grant. "In contrast, superinfection has not appeared in people who have had the disease for many years, as our couples have." The possibility that superinfection may be restricted to a short window period after the development of HIV has been suggested by experimental studies in nonhuman primates. In addition, a recent mathematical analysis demonstrated that superinfection restricted to a short window period after HIV seroconversion could account for the high prevalence of recombinant and dual infections observed in some parts of the world. This analysis has just been published in the July 23, 2004, issue of AIDS, the journal of the International AIDS Society, as a paper titled "HIV-1 Superinfection and Viral Diversity," by Grant and investigators Kimber L. Gross and Travis C. Porco of the San Francisco Department of Public Health. "Studies are warranted to better understand why superinfection among patients who have had HIV for a long time is rare," Grant explains. "The mechanisms preventing superinfection may include specific or non-specific antiviral immune responses or viral interference. If there is indeed an immune response at play, it's reasonable to investigate the possibility of inducing that response with a vaccine that can be made available to high-risk HIV-negative individuals."