Comparison of Epidemiological Methods for Estimation of Hepatitis B Incidence and Residual Risk for Blood Donors in Southern Brazil

Table 3

HBV incidence and residual risk for stand-alone HBsAg in repeat blood donors in southern Brazil, 2004–2006.

Parameter	Value
Number of HBsAg seroconverting donors	1
Median of interdonation intervals (days)	329
Probability of transient antigenaemia^1	0.1915
Probability of detecting HBV seroconversion by stand-alone HBsAg test^2	0.1840
Time at risk (person-years) for HBsAg seroconverting donors	0.45
Time at risk (person-years) for all repeat donors	54788.73
Incidence per 100.000 per year (95% CI)^3	1.825; (0.00, 6.73)
Adjustment factor^4	5.43
Adjusted incidence per 100.000 per year (95% CI)	9.91; (0.00, 36.54)
Residual risk (95% CI)^5	1 : 62482; (1 : 16946, 1 : ∞)

¹Assuming 63 days of average duration for transient antigenaemia [8], that is, 63/329.
²Assuming 75% of blood donors with ELISA detectable HBsAg8.
³Confidence interval.
⁴Reciprocal value of the probability of detecting HBV seroconversion by stand-alone HBsAg test, that is, 1/0.184=5.43.
⁵Assuming Poisson distribution for one HBsAg seroconverting case.