Background: We have previously reported a HIV-1 subtype A infection in a community of injection drug users (IDUs) in Karachi, Pakistan. We now show that this infection among the IDUs may have originated from a single source.
Methods: Phylogenetic analysis was performed of partial gag sequences, generated using PCR, from 26 HIV-positive IDU samples.
Results: Our results showed formation of a tight monophyletic group with an intra-sequence identity of < 98% indicating a "founder effect". Our data indicate that the HIV-1 epidemic in this community of IDUs may have been transmitted by an HIV positive overseas contract worker who admitted to having contact with commercial sex workers during stay abroad.
Conclusion: Specific measures need to implemented to control transmission of HIV infection in Pakistan through infected migrant workers.