In order to estimate HBV incidence accurately, an HBsAg yield window of 44 days was used as described in a previous study . The ratio of HBsAg new infection rate of donations from first-time donors to repeat donors was 6.97, 6.57, 6.94, 4.41, 9.04 and 15.43, at the Hefei, Dalian, Changzhi, Kaifeng, Mianyang and Fujian Blood Centers, respectively. Overall, the estimated incidence rate was 213.44, 161.59, 989.80, 278.05, 125.31 and 352.19 (per 100,000 person-years) in Hefei, Dalian, Changzhi, Changzhi, Kaifeng, Mianyang and Fujian, respectively (see Table 7).Table 7HBsAg Incidence by Blood Center/ Bank Among First-Time and Repeat DonorsBlood CenterFirst-TimeRepeatRatio ofa HBsAg new infection rateYield Window(year)Incidence(per 105 py)Number of HBsAgConfirmed Positive, Anti-HBc NegativeIncidence(per 105 py)Number of HBsAgConfirmed Positive, Anti-HBc NegativeYield Rate(per 105 py)Incidence(per 105 py)Hefei13315.3925.4345.256.970.12213.3Dalian36281.5225.1442.856.570.12161.59Changzhi52347.34940.59338.236.940.12989.80Kaifeng10372.89210.1584.564.410.12278.05Mianyang2261.1453.4728.899.040.12125.31Fujian6640.1924.9841.1915.430.12352.19Total72773.492211.9399.427.780.12197.38 aThe HBsAg new infection rate in repeat donors is the HBsAg+/HBc antibody- prevalence, and the incidence for HBV infections in first-time donors is equal to the incidence for HBV infections in repeat donors multiplied by the ratio of HBsAg new infection rate (the ratio of HBsAg new infection rate = HBsAg new infection rate of first-time donors over HBsAg new infection rate of repeat donors). The overall incidence for HBV infections in all donors is the percentage of incidence in first-time donors plus the percentage of incidence in repeat donors. For Hefei, 315.18 × 10−5 × 0.6226 (Number of first-times / number of first-times + number of repeats = 60,812 / 97,668) + 45.22 × 10−5 × 0.3774 = 196.23 × 10−5 + 17.07 × 10−5 = 213.3 × 10−5)The residual risk calculation model used in this study is one of the more suitable computational models in the absence of nucleic acid detection. Based on the results of the last two blood tests, it is possible to extrapolate whether the recent donors have a new infection. However, for the first-time donors, the new infection ratio cannot be determined or calculated directly. Therefore, this model is adopted to indirectly establish the incidence and residual risk of the first-time donors