CD4 and syphilis: This is consistent with previous studies that showed that HIV co-infection with syphilis is associated with systemic inflammation characterised by elevations in CRP levels.32 The lower CD4 cell counts in participants with co-infections could be the consequence of immune activation.33 We found lower plasma iron levels at baseline in participants with co-infections, likely due to the pro-inflammatory state, which results in the liver releasing hepcidin which in turn signals the ferroportin channels to block the efflux of iron into circulation, resulting in reduced plasma iron levels.34