RESUMO
Background & objectives: Nucleic acid amplification test (NAT) in blood donor screening not only detects window period (WP) donors but also those with chronic occult infections which are negative by routine serological screening. This study was conducted to determine the time trend of NAT positivity and seroprevalence of transfusion-transmitted infections (TTIs) through a period of six years and evaluate the strength of NAT as a supplementary test in identifying the cryptic carriers in blood donor population. Methods: A total of 1,01,411 blood donations were screened between January 2011 and December 2016 by the ELISA and individual donor (ID) NAT Procleix Ultrio Plus Assay. Additional molecular and serological assays were done on the NAT yield samples to differentiate the type of cryptic carriers. Results: NAT yields comprised 0.05 per cent (50/101411) of the total samples tested with a yield rate of 1/2028. Hepatitis B virus (HBV) contributed to 80 per cent of the total NAT yields and the rest 20 per cent due to hepatitis C virus (HCV). Majority of HBV NAT yields (75%) were from chronic occult donors and 25 per cent were WP donors. Both HBV and HCV NAT yields had a wide range of viral count. There was no HIV NAT yield. A significant decline in the prevalence rate of TTIs through the study period of six years was observed. Interpretation & conclusions: The cryptic infections found in blood donors increase the risk of TTIs. Blood screening by both serology and NAT can reduce this threat.