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is epidemiologically relevant. Indeed, SARS-CoV evolved during the course of the SARS outbreak in China (12). Similarly, influenza is perpetuated in the human population by the evolution of new antigenic variants every year (Robin Bush, University of California, Irvine) (13). Even if the transmissibility of an emerging disease is initially below the threshold necessary to sustain it in a population, the potential for the organism’s evolution to higher levels may exist (14,15). Thus, one should not become complacent about diseases that are repeatedly introduced through zoonosis, but teeter on the edge of sustainability within the human population. The success with which WHO coordinated the global collaboration in containing SARS galvanized the World Health Assembly to grant WHO greater authority to verify outbreaks, conduct investigations of outbreak severity, and evaluate the adequacy of control measures. The outcome of this new authority will depend on integrating the expertise of public health officials, medical doctors, and epidemiologists worldwide with guidance from disease transmission models. The SARS outbreak demonstrated that an epidemic in one part of the world is not just an individual nation’s problem but a global problem.