Table 7.

HBsAg Incidence by Blood Center/ Bank Among First-Time and Repeat Donors

Blood Center	First-Time		Repeat			Ratio ofa HBsAg new infection rate	Yield Window (year)	Incidence (per 105 py)
	Number of HBsAg Confirmed Positive, Anti-HBc Negative	Incidence (per 105 py)	Number of HBsAg Confirmed Positive, Anti-HBc Negative	Yield Rate (per 105 py)	Incidence (per 105 py)
Hefei	13	315.39	2	5.43	45.25	6.97	0.12	213.3
Dalian	36	281.52	2	5.14	42.85	6.57	0.12	161.59
Changzhi	5	2347.34	9	40.59	338.23	6.94	0.12	989.80
Kaifeng	10	372.89	2	10.15	84.56	4.41	0.12	278.05
Mianyang	2	261.14	5	3.47	28.89	9.04	0.12	125.31
Fujian	6	640.19	2	4.98	41.19	15.43	0.12	352.19
Total	72	773.49	22	11.93	99.42	7.78	0.12	197.38

^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