Migration patterns of HIV-1 subtype B virus in Northern Italy.

Gene flow analysis is used to identify the migration patterns of viruses within a geographical area and /or in different populations. 883 HIV-1 B subtype pol gene sequences were analyzed. The gene analysis among different geographical areas of the Bergamo district and from different transmission risk groups showed 25% of the observed gene flow was from people living in the north valleys to lowland and 40.5% from a heterosexual risk group to injecting drug users. Injecting drug users seem to be the central link, mercenary sex being the common route of transmission (and gene flow) between this group and both heterosexual and homosexual individuals.