Prevalence, incidence and residual risk of transfusion-transmitted hepatitis C virus and human immunodeficiency virus after the implementation of nucleic acid testing in Italy: a 7-year (2009-2015) survey

Background. In Italy nucleic acid testing (NAT) became mandatory for hepatitis C virus (HCV) in 2002 and for human immunodeficiency virus (HIV) and hepatitis B virus in 2008. The aim of this study was to monitor the incidence and prevalence of HIV and HCV infections in Italian blood donors and the current residual risk of these infections after the introduction of NAT. Materials and methods. The Italian national blood surveillance system includes data from tests used to screen for transfusion-transmissible infections. During the period of this survey (2009-2015), the NAT methods used were the transcription-mediated amplification test, for individual donor testing, and polymerase chain reaction analysis, mainly for pools of six donors. Prevalence and incidence were calculated. Three published formulae were applied to estimate the residual risk (the window period ratio model and the formulae recommended by the European Medicines Agency and the World Health Organization). Results. Overall, 12,258,587 blood donors and 21,808,352 donations were tested for HCV and HIV. The prevalence of HCV decreased from 110.3x10(5) to 58.9x10(5) in years 2009 and 2015, respectively, while that of HIV remained stable over time (15.5x10(5) vs 15.4x10(5)). The incidence of HCV decreased from 3.19x10(5) in 2009 to 1.58x10(5) in 2015, while the incidence of HIV did not show any significant fluctuations (average incidence 4.39x10(5)). The residual risk of a viraemic unit entering the blood supply was estimated to be 0.077x10(6) or 1 in 12,979,949 donations for HCV and 0.521x10(6) or 1 in 1,917,250 for HIV, according to the window period ratio model, and lower with the other two formulae. Discussion. HCV infection has declined over time in both first-time and repeat donors, while the data for HIV infection are stable. All three methods employed in this study showed that the residual risk of transmitting HCV or HIV through an infected blood unit is currently very low in Italy, but there are considerable differences in estimates between methods. Thus, harmonisation of these methods is advisable.