Molecular Tracing of the Geographical Origin of Human Immunodeficiency Virus Type 1 Infection and Patterns of Epidemic Spread Among Migrants Who Inject Drugs in Athens.

Background. High numbers of human immunodeficiency virus type 1 (HIV-1) infections among people who inject drugs (PWID) have been diagnosed in Athens, Greece, since 2011. We aimed to trace the geographic origin of HIV-1 infection for migrants who inject drugs and to investigate whether transmissions occur more frequently among migrants than among Greek nationals. Methods. Multiple cross-sectional studies were pooled to assemble all persons diagnosed with HIV-1 in Greece between 1 January 2011 and 31 October 2014. Phylogenetic analyses used maximum likelihood estimation. The hypothesis of ethnic compart-mentalization was tested by reconstructing ancestral states of characters at the tips using the criterion of parsimony over a set of bootstrap trees. Results. Of 2274 persons, 38.4% were PWID. Phylogenetic analyses showed the existence of 4 major PWID-specific local transmission networks (LTNs): CRF14_BG (437 [58.6%]), CRF35_AD (139 [18.6%]), subtype B (116 [15.6%]), and subtype A (54 [7.2%]). Of 184 non-Greek PWID, 78.3% had been infected within the PWID-LTNs. For 173 (94.3%), the origin of their infection was assumed to be in Greece (postmigration). For PWID infected within LTNs, transmissions for subtype A and CRF14_BG occurred more frequently among migrants than would be expected by chance (phyloethnic study). Conclusions. Our analysis showed that the majority of infections among migrants occurred postmigration. The existence of significant transmission networking among migrants highlights that this population is a priority for HIV prevention. As molecular analysis can estimate the probable country of HIV infection, it can help to inform the design of public health strategies.