A research group from Ottawa reported on superinfection. Superinfection with a second strain of HIV-1 is not yet well described. The authors describe a case of an antiretroviral naive male (Patient A) who had non-progressive HIV infection for greater than 8 years and undetectable plasma viremia prior to the initiation of a sexual relationship with a man with advanced HIV disease and extensive antiretroviral exposure (Patient B). Shortly after sexual contact, Patient A developed an increasing viral load and a declining CD4 T cell count.

HIV RNA from cryo-preserved peripheral blood mononuclear cells (PBMC) or plasma specimens from Patient A (sample A1; PBMC before "new" exposure, and sample A2; plasma after "new" exposure) and Patient B (sample B; plasma) were PCR amplified. PCR products were cloned into a TA vector (Invitrogen Corp.) and re-amplified by PCR for sequencing. HIV-1 cDNA from 41 clones (14 from sample A1, 16 from sample A2 and 11 from sample B) from the protease (PR) gene and from 35 clones (15 from sample A1, 12 from sample A2 and 8 from sample B) from the reverse transcriptase (RT) gene were directly sequenced and analyzed with the TreeMaker program utilizing PHYLIP programs Dnadist (Distance Matrix program), Neighbor (treefile generator) available on line at http://hiv-web.lanl.gov, producing a phenogram for each PR and RT.

By phylogenetic analysis, all clones from sample A1 were unrelated to those from the sample B at both the PR and RT genes. Analysis of sample A2 revealed significant homology to sample B in 5 of 16 PR clones and 4 of 12 RT clones. All other clones from sample A2 were closely related to clones from sample A1. Phylogenetic analyses of the PR and RT regions directly sequenced from 12 unselected patients revealed that these were easily distinguishable from all sequences from samples A1, A2 and B.

They described what appears to be the first report of HIV-1 superinfection and that this was followed by more rapid progression of HIV disease. The fact that HIV-1 infection does not necessarily result in resistance to subsequent infection has significant public health and epidemiological implications and emphasizes the importance of safer sexual practices between HIV-infected persons.