In 2006, Yale researchers announced the presence of extensively drug resistant tuberculosis (XDR-TB) in a remote hospital in South Africa. Fifty-two of 53 patients had died within a month of being seen; most were HIV positive. Experts warned of a new, frightening infectious disease: this "virtually untreatable," "rapidly fatal," "extreme" illness was poised to "imperil millions." On the surface, it appeared that XDR-TB was a new disease defined with great scientific clarity. Closer inspection, however, reveals that the definition of this disease was subject to intense debate grounded both in the politics of biomedical science as well as in the science itself. My dissertation will investigate two central questions. First, I will use the emergence of XDR-TB to study the process of scientific inquiry through which scientists engage in the difficult task of defining scientific categories that also have profound policy implications. Second, I will examine the impact these decisions have had on the realities of medical care on a local level. In other words, what does it mean to be suffering from an illness of global significance? In the context of this study, this will mean telling the story of how the deaths of 52 patients in Tugela Ferry received the attention of the international community and exploring the effects this international interest has had on the South African experience of TB illness. This study is situated within the broader discursive field of global health and will shed light on the international production of competitive science, the mobilization of science in making effective global health policy, and the effects of policies that impact patient care.