Introduction
Founder effects, genetic drift and recombination associated with
the global spread of HIV-1 infection have given rise to genetically
distinct viral strains referred to as ‘subtypes’ and ‘circulating
recombinant forms’ [1]. HIV-1 genetic diversity may impact on
disease progression and response to antiretroviral therapy, and has
implications for vaccine development [2]. It is therefore important
to monitor changes in the genetic and geographic complexity of
the HIV-1 epidemic, and to identify the processes that drive these
changes.