Estimating the date of hepatitis C virus infection from patient interviews and antibody tests on stored sera

OBJECTIVES: Studies on the natural history and outcome of chronic hepatitis C virus (HCV) infection differ regarding the proportion of persons who develop serious sequelae over time. Most of these studies use an estimated date of HCV infection based on risk factor data obtained from patient interviews. The date of HCV infection is often estimated using the year of a pre-1992 blood transfusion (BT), or the first year of injecting drug use (IDU). We sought to determine the accuracy of these dates obtained by interview. METHODS: We compared BT dates reported by patients in a long-term HCV outcome study to dates confirmed in a BT-Lookback project, and also compared the reported first year of IDU to seroconversion dates estimated from HCV tests on historical sera. RESULTS: Of 28 BT recipients who were interviewed in the HCV outcome study and identified in the Lookback project, 14 (50%; 95% Cl: 31-69%) were unaware they had received a BT. Of 25 persons identified in the BT-Lookback project with historical sera available, 9 (36%; 95% Cl: 19-57%) had anti-HCV results that did not correlate with their confirmed BT date. Of 216 persons with a history of IDU and historical serum samples available, 66 (31%; 95% Cl: 25-37%) had anti-HCV results that did not correlate with their reported first year of IDU. CONCLUSIONS: Inaccuracies in the length of HCV could occur in outcome studies that rely on patient recall of risk-factor history. Statistical methods that incorporate the uncertainty in assigning infection date are needed.