DURATION OF TIME FROM ONSET OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 INFECTIOUSNESS TO DEVELOPMENT OF DETECTABLE ANTIBODY

Background: For persons newly infected with the human immunodeficiency virus type 1 (HIV-1), the time from the onset of infectivity to the d evelopment of detectable HIV-1 antibody is unknown. Persons who donate blood during this period account for nearly all instances of HIV-1 tr ansmission from HIV-1 antibody-screened blood transfusions. Study Desi gn and Methods: To estimate the window period from infectivity to HIV- 1 antibody positivity, 701 HIV-1-seropositive blood donors who made a previous seronegative donation at 40 United States blood centers were studied. The HIV-1 antibody status was determined for at least one rec ipient of blood from the seronegative donation preceding the seroposit ive donation made by 182 of the 701 donors. Results: There were 39 ser opositive recipients of blood from these 182 donors. Three donors were excluded from further analysis because the seropositive recipients of their blood had other HIV-1 risk factors or had HIV-1 infection befor e transfusion. The final study population comprised the remaining 179 donors, of whom 36 (20%) transmitted HIV-1 infection to recipients. Wh en the interval between the seropositive donation and the preceding se ronegative donation was less than 180 days, 46 percent of the donors t ransmitted HIV-1. In contrast, when that interval exceeded 540 days, o nly 2 percent transmitted HIV-1. A mathematical model was developed to explain the relationship between the probability that the previous se ronegative donation occurred during the donor's window period of infec tiousness, and hence transmitted HIV-1, as a function of both the wind ow period and the duration between the seropositive and previous seron egative donations. This model indicated that the transmission data wer e most consistent with an average window period of 45 days. Assuming a log-normal window period distribution, it was estimated with 95 perce nt certainty that at least 90 percent of persons had a window period o f less than 141 days. Conclusion: window period averages 45 days, with few, if any, donors remaining infectious and seronegative for longer than 6 months.