Phylogenetic analysis of multiple heterosexual transmission events involving subtype B of HIV type 1

Between 1996 and 1999 thirteen cases of HIV infection were detected in Donc aster, a small town in the north of England (population similar to 250,000) , A complex network of shared sexual histories involving local nightclubs l inked these cases, with the only known risk factor being heterosexual inter course. A series of frozen blood samples was collected in 1998-1999 and amp lified by PCR to generate full-length gp120 clones. Sequencing demonstrated that all the transmission events in this heterosexual group involved the B subtype of HIV-1, When relationships between the samples were assessed it became clear that these 13 cases represented at least three separate strain s of HIV-1, indicating that HIV is well established in this community. Elev en of the 13 cases were related, forming two distinct groups. Further inves tigation revealed that one group contained five patients whose general heal th was good and who were not receiving HAART, In contrast, the second group of six patients, including the putative index case, were symptomatic, rece iving HAART, and may have been infected with a CXCR-4-utilizing virus. Seve ral of the cases that were linked by genetic criteria were not linked by co ntact tracing, implying that further undiagnosed cases may exist in this co mmunity, To our knowledge, this is the largest outbreak of HIV studied with in the heterosexual community in the United Kingdom to date, suggesting tha t this route of infection is becoming more common within the United Kingdom .