A method for estimating incidence rate of infectious diseases among first-time blood donors

BACKGROUND: In certain circumstances, there is no method for estimating incidence based on testing results on a single blood sample from first-time blood donors, severely limiting the ability to assess the residual risk of blood-borne infections among this donor subpopulation. STUDY DESIGN AND METHODS: Incidence rates were estimated for human immunodeficiency virus (HIV) and hepatitis C virus (HCV) among first-time donors using the formula (P-2 - P-1)/D, where P-1 is the prevalence among blood donations from first-time donors of the minimum eligible ages for donation, P, is the prevalence among donations from first-time donors of an older age group, and D is the age difference (in years) between the older and younger donor groups. RESULTS: Estimating incidence among first-time donors using the proposed method based on a single test for anti-HCV produced similar results to those based on HCV nucleic acid test (NAT) yield cases, by sex and in different periods. Comparison of the proposed method with HIV NAT yield also showed similar results although the small number of HIV NAT yield cases limits interpretation. CONCLUSIONS: The proposed method provides an alternative way for estimating incidence of certain blood-borne infections among first-time donors, provided that our assumptions are met. It helps residual risk assessment in donor populations where first-time donors account for most of the donations and only one test result is available for each donor.