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 Doncaster, a small town in the north of England (population approximately 250,000). A complex network of shared sexual histories involving local nightclubs linked these cases, with the only known risk factor being heterosexual intercourse. A series of frozen blood samples was collected in 1998-1999 and amplified 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 strains of HIV-1, indicating that HIV is well established in this community. Eleven of the 13 cases were related, forming two distinct groups. Further investigation revealed that one group contained five patients whose general health was good and who were not receiving HAART. In contrast, the second group of six patients, including the putative index case, were symptomatic, receiving HAART, and may have been infected with a CXCR-4-utilizing virus. Several of the cases that were linked by genetic criteria were not linked by contact tracing, implying that further undiagnosed cases may exist in this community. To our knowledge, this is the largest outbreak of HIV studied within the heterosexual community in the United Kingdom to date, suggesting that this route of infection is becoming more common within the United Kingdom.