Limited HIV-1 Superinfection in Seroconverters from the CAPRISA 004 Microbicide Trial

HIV-1 superinfection (SI) occurs when an infected individual acquires a distinct new viral strain. The rate of superinfection may be reflective of the underlying HIV risk in a population. The Centre for the AIDS Programme of Research in South Africa (CAPRISA) 004 clinical trial demonstrated that women who used a tenofovir-containing microbicide gel had lower rates of HIV infection than women using a placebo gel. Women who contracted HIV-1 during the trial were screened for the occurrence of superinfection by next-generation sequencing of the viral gag and env genes. There were two cases (one in each trial arm) of subtype C superinfection identified from the 76 women with primary infection screened at two time points (rate of superinfection, 1.5/100 person-years). Both women experienced a >0.5-log increase in viral load during the window when superinfection occurred. The rate of superinfection was significantly lower than the overall primary HIV incidence in the microbicide trial (incidence rate ratio [IRR], 0.20; P = 0.003). The women who seroconverted during the trial reported a significant increase in sexual contact with their stable partner 4 months after seroconversion (P < 0.001), which may have lowered the risk of superinfection in this population. The lower frequency of SI compared to the primary incidence is in contrast to a report from a general heterosexual African population but agrees with a study of high-risk women in Kenya. A better understanding of the rate of HIV superinfection could have important implications for ongoing HIV vaccine research.