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Background: It is assumed that in seronegative donations pool still lag some infected donations. These are donations of blood donors who are in pre-seroconversion window period (WP) of infection or have occult infection or are infected with viral variants that can not be detected by standard tests. Mathematical models are developed to assess the residual risk (RR) for viral transfusion-transmissible infections. Monitoring and trend analysis of RR are used for method selection and testing optimization, thereby for increasing the safety of blood. From March 1, 2013 mandatory test for blood donors in Croatia, with serology tests, is ID-NAT triplex test (HBV, HCV, HIV-1). Aims: To calculate and analyze trend of RR for HBV, HCV and HIV infections by seronegative blood donations of repeat blood donors in Croatia for two time periods: I. 1997 – 2004 and II. 2005 - 2012. Methods: Two selected time periods differed according to the type of used tests for HIV, HBV and HCV infection. In the first time period blood (1.258.992 donations) was tested for HBsAg, anti-HCV and anti-HIV assays with the WP of 56, 65 and 22 days, respectively, and in the second time period blood (1.356.991 donations) was tested for HBsAg, anti-HCV and HCV Ag and HIV Ag/Ab tests with the WP of 38, 30 and 16 days, respectively. For RR calculation we used a mathematical model from Schreiber et al., 1996. For this two time periods we recorded 29 and 15 seroconversions, respectively, 14 HBV, 23 HCV and 7 HIV. HBV RR is additionally corrected for occult HBV infection (OBI) in a way that to the WP of 56 or 38 days, respectively, were added 14 days, according to Seed et al, 2005. Results: RR are shown in the table. Conclusion: Results show the reduction of RR for HBV, HCV and HIV infections by seronegative blood donations in Croatia, which is mostly driven by increased tests sensitivity, decreased incidence of viral infections in repeat blood donors and a more efficient pre-donation blood donor screening. The most significant decline was recorded for HCV infection from 1:65.000 to 1:900.000 blood donations, and appeared after the termination of taking blood from a soldier recruits. In the first time period there were 19 HCV seroconversions and in the second time period only 4 of it. The RR for HIV infection is very low, but does not show a distinct trend of decline, as HCV and HBV. Correction for HBV RR for donors with occult HBV infection risk is 20% higher in the first and 30% in the second examined period. The RR by the introduction of ID-NAT should be negligible, from 1:600.000 for HBV to 1:2.000.000 and more for HIV and HCV. |
