Research methods have previously been described (Nikolopoulos et al., 2016 (link), 2017 (link)), so we do so only briefly here.
Setting: The study took place (6/2013–7/2015) in Athens, Greece, where an HIV outbreak among people who inject drugs (PWID) began in 2011 (Paraskevis et al., 2011 (link), 2013 (link), 2015 (link); Nikolopoulos et al., 2015b (link)).
Laboratory Methods: HIV testing used a microparticle anti-HIV-1/2 EIA (AxSYM HIV-1/2 gO, Abbott) confirmed by Western Blot (MP Diagnostics). All HIV+ participants were tested by Limiting Antigen Avidity Assay (LAg; SediaTM Biosciences Corporation) (Duong et al., 2012 (link), 2015 (link); Nikolopoulos et al., 2017 (link)). This test is based on antibody maturation to categorize HIV infection as “recent” or “long-standing.” An Optical Density (ODn) score of 1.5 was used as a cut-off for recent infection, with a median of three ODn values ≤1.5 indicating recent infection. This corresponds to a window period of 130 days (Duong et al., 2015 (link)). HIV RNA was quantified for all HIV-positive samples with Artus HI Virus-1 RG RT-PCR (Qiagen). Antibody-negative samples in social networks were tested for viremia (and thus acute infection) in pools of 10.
Setting: The study took place (6/2013–7/2015) in Athens, Greece, where an HIV outbreak among people who inject drugs (PWID) began in 2011 (Paraskevis et al., 2011 (link), 2013 (link), 2015 (link); Nikolopoulos et al., 2015b (link)).
Laboratory Methods: HIV testing used a microparticle anti-HIV-1/2 EIA (AxSYM HIV-1/2 gO, Abbott) confirmed by Western Blot (MP Diagnostics). All HIV+ participants were tested by Limiting Antigen Avidity Assay (LAg; SediaTM Biosciences Corporation) (Duong et al., 2012 (link), 2015 (link); Nikolopoulos et al., 2017 (link)). This test is based on antibody maturation to categorize HIV infection as “recent” or “long-standing.” An Optical Density (ODn) score of 1.5 was used as a cut-off for recent infection, with a median of three ODn values ≤1.5 indicating recent infection. This corresponds to a window period of 130 days (Duong et al., 2015 (link)). HIV RNA was quantified for all HIV-positive samples with Artus HI Virus-1 RG RT-PCR (Qiagen). Antibody-negative samples in social networks were tested for viremia (and thus acute infection) in pools of 10.
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