Incidence of seroconversion to positivity for hepatitis C antibody in repeat blood donors in England, 1993-5.

OBJECTIVE To estimate the rate of seroconversion to positivity for hepatitis C antibody in repeat blood donors in England and to describe the probable routes of infection in these donors. DESIGN Retrospective survey of blood donors becoming positive for hepatitis C antibody and of the results of donation testing. SETTING The 14 blood centres in England. SUBJECTS All repeat donors giving blood between January 1993 and December 1995. MAIN OUTCOME MEASURES Number of donors developing hepatitis C between donations during the three years of testing for hepatitis C antibody at English blood centres and the rate of seroconversion among repeat blood donors. Probable routes of infection. RESULTS 14 donors during 1993-5 fulfilled the case definition for seroconversion to positivity for hepatitis C antibody. The estimated seroconversion rate for infection with hepatitis C in repeat donors was 0.26 per 100 000 person years (95% confidence interval 0.15 to 0.43). Counselling after diagnosis found that four of these donors had risk factors specified in the criteria excluding people from giving blood but these factors had not come to light before donation. Another of the donors who seroconverted had a risk factor that has since been included in the exclusion criteria. Heterosexual intercourse was considered to be the most likely route of infection for five of the 14 donors. CONCLUSIONS The rate of seroconversion for positivity to hepatitis C antibody in repeat blood donors in England was extremely low. During 1993-5 fewer than 1 in 450 000 donations were estimated to have come from repeat donors who had become positive for hepatitis C antibody since the previous donation.