I stumbled upon a short story some months ago on a website. It's written by a black female author, and it's about a boy who I think was the subject of some experiments (he can cure diseases or something) and either escapes or dies. We know all of this because we read it as his diary or letters between doctors (it's epistolary).
Also it was collected in This Year's Best Science Fiction but I don't know the issue. I suspect it's post 2000s. Any ideas on either author or title?