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Nucleic acid testing (NAT) was implemented in Poland in 1999 for screening of plasma for fractionation and for all blood donors in 2002. To analyze seronegative NAT‐positive samples representing hepatitis C virus (HCV) window‐period (WP) in the years 2000 to 2016 and to determine infection outcome. We analyzed results of 17 502 739 donations screened in minipools (6‐48) or individually. Index samples underwent viral load (VL) quantification, genotyping and Ag, and anti‐HCV re‐testing using chemiluminescence (CMIA), electrochemiluminescence (ECLIA), and fourth‐generation enzyme‐linked immunosorbent assay (IV EIA) assays. HCV‐seronegative infections were identified in 126 donations (7.2/mln donations; 95% confidential intervals, 6.0‐8.6). Frequency of NAT yields was decreasing over time. Of the initial 126 seronegative index cases 106 were retested: 32.1% were reactive in IV EIA, 11.3% in ECLIA, and 1.9% in CMIA. The lowest VL correlated with absent anti‐HCV and HCV Ag, while VL was highest when the antigen was detectable and then it decreased when anti‐HCV appeared at a level detectable by sensitive third generation tests while retesting. The proportion of genotype 1 was 38.9% in samples positive only for HCV RNA and 71.4% in samples that were anti‐HCV reactive in re‐testing. In parallel, genotype 3 frequency was 50% in the former group and 21% in the latter. NAT is an effective measure to limit HCV transmission by transfusion and IV EIA seems to have higher clinical sensitivity than ECLIA. Samples representing likely successive phases of early HCV infection were characterized by different genotype distribution probably due to very early elimination of genotype 3., Highlight NAT is highly effective in prevention of transmission of HCV seronegative infections.In nearly 7% of followed up donors antibodies appeared later than 50 days after index donation.The highest clinical sensitivity was demonstrated by the IVth generation tests.Among the third generation assays, ECLIA showed higher sensitivity than CMIA.Samples representing likely successive phases of early HCV infection demonstrated different genotype distribution.

The study assessed the incidence of HBV markers (HBsAg, anti-HBc, anti-HBs) important for determination of the risk of reactivation of infection, with particular interest of occult infection (presence of HBV DNA in the absence of HBsAg) in patients treated at the Institute of Hematology and Transfusion Medicine. Anti-HBc frequency was correlated with the age and sex of patients. HBsAg was detected in 16/468 examined patients, 98/468 (21%) were anti-HBc positive. HBV DNA was detected in 41/98 anti-HBc positives; in 13 simultaneously with HBsAg. 28 patients had occult HBV infection (HBV DNA+/HBsAg). Antibody to HBsAg was detected in 163/430 (38%) patients, 81 out of them on protective level (100 IU/l). It was shown that occult HBV infection occurs in approximately 6% of patients. In most of them the protective levels of anti-HBs are detected.