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Wainberg and colleagues1 argue for a change in blood donation policy that would allow some low-risk men who have had sex with other men (MSM) to donate. They cite an estimate based on modelled data that suggested that shortening the MSM deferral period from lifetime to one year would result in one additional HIV-infected unit of blood escaping detection in Canada every 16 years, or one additional unit per 11 000 000 transfusions.2 This 2003 estimate, however small, still represents a substantial overestimate of risk. When the rates of laboratory error used for modelling were updated to more current levels, the risk estimates decreased 10-fold.3 This risk calculation represents an estimate for the first year that newly eligible donors would enter the donor pool; they cannot be accurately extended over longer periods without adjusting for the effects of repeat donations. Tests of new donors represent prevalence screens, detecting both recent and long-standing infections. Because repeat donors have previously been tested, the test represents an incidence screen for new infection since the previous donation. Therefore, repeat donors typically have rates of infection half those of first-time donors.4
As testing has improved dramatically and the epidemic has shifted, other countries have shortened their deferral periods for blood donation. Indeed, the reports of international blood donation policies in Wainberg and colleagues’ article are already outdated. Last year, New Zealand shortened its MSM deferral period from 10 years to 5 years, and South Africa from 5 years to 6 months.
For the full letter, go to: www.cmaj.ca/cgi/eletters/cmaj.091476v1#494257