ESTIMATED RATE OF HIV-1-INFECTIOUS BUT SERONEGATIVE BLOOD DONATIONS IN BANGKOK, THAILAND

Objectives: To determine HIV seroprevalence and incidence among variou s blood donor types, and to estimate the rate of window-period blood d onations. Design: Retrospective cohort from computerized donor records . Methods: Records were analysed from all 60 483 donors (contributing 97 464 donor units) at a public university teaching hospital blood ban k in Bangkok, Thailand, from 1 January 1990 to 30 June 1993. Annual HI V incidence among 14 482 repeat donors who were HIV-seronegative on th eir first donation was calculated assuming equal probability of seroco nversion between last seronegative and first seropositive donations. T o estimate the probability of window-period donations, we assumed that the time from HIV infectivity to onset of detectable antibody was 45 days. Results: In 1990, HIV incidence calculated for all repeat donors was 307 per 100 000 person-years; the probability of a window-period donation was 38 in 100 000 donations or one in 2644 donations. During 1991-1993, this probability decreased by one-half. However, one-time d onors were more than twice as likely as repeat donors to be HIV-l-sero positive. Conclusions: The rate of HIV window-period blood donations a mong Thai repeat donors was relatively high compared with that in deve loped countries and was probably even higher among one-time donors. Im proved donor deferral criteria are needed in Thailand.