Panels of sequential samples obtained by plasmapheresis from US plasma donors who became infected with HIV-1, HBV or HCV and control subjects were purchased from Zeptometrix Corporation and SeraCare Life Sciences and were stored at 280uC before use. Details of the panels and methods used for analysis of HIV-1, HBV and HCV viral loads are as described [14] . Each plasma panel included samples collected prior to detection of plasma viremia through to seroconversion. The plasma panels from HIV-infected individuals were temporally aligned relative to a common time origin (T 0 ), defined as the time point when the viral load first reached detectable levels (.100 viral RNA copies ml 21 ), as described previously [14] . The median and range duration of observation prior to the first detectable HIV RNA level (T 0 ) for the 19 panels used in this study was 21 days with a range of 7 to 58 days.