Figure 1

Flowchart showing follow-up status of subjects with respect to biological measurements and survival over the course of the study. At some time points subjects were known to be alive e.g. they were seen at later time points, but measurements were not taken from them. ^a After 2006 biological measurements were not taken and so data on seroconversions not available between 2006 and 2009. ^b Subjects who had died by mid-2009. ^c Known to be alive at latest census in 2009.