Detailed Molecular Surveillance of the HIV-1 Outbreak Among People who Inject Drugs (PWID) in Athens During a Period of Four Years.

Background: New diagnoses of HIV-1 infection among people who inject drugs (PWID) increased significantly during 2011 in Athens.
Objective: Our aim was to investigate the patterns of HIV epidemic spread among PWID and to estimate the transmission dynamics for the major local transmission networks (LTNs).
Methods: We analyzed sequences from 2,274 HIV-infected subjects sampled in Greece during 01/01/2011-31/10/2014. Of specimens in our sample, 874 sequences were isolated from HIV-infected PWID. Phylodynamic analysis was performed using birth-death serial skyline models.
Results: Phylogenetic analysis revealed that the majority of sequences from PWID (N=746, 85.4%) fell within four LTNs: CRF14_BG (N=456, 58.3%), CRF35_AD (N=149, 19.1%), subtype B (N=118, 15.1%) and A1 (N=59, 7.5%). In addition to PWID, we also found that sequences from 36 non-PWID belonged to the LTNs corresponding to cross-group transmissions. Based on the estimated plots of the effective reproductive number (Re) over time, subtype A1 and CRF35_AD LTNs showed a sharp increase before and during 2011 (maximum value of Re=3.0 and Re=4.6, respectively). For subtype B and CRF14_BG LTNs, the Re was increasing until the end of 2012 (maximum value of Re=3.2 and Re=3.0, respectively).
Conclusion: HIV transmissions within subtype A1 and CRF35_AD LTNs increased sharply during the early stage of the outbreak, in contrast to subtype B and CRF14_BG. A significant reduction in the number of infections was estimated on all transmission networks from the beginning of 2013 onwards. Prevention measures that took place in the Athens metropolitan area at the end of 2012 including also the ARISTOTLE program may explain this decrease.
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