About the Authors

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Competing Interests

LEC is a recipient of a Pfizer Pharmaceuticals Fellowship in Infectious Diseases, 2005–2008. PHE and LR declare that they have no competing interests.

Author Contributions

LEC and LR designed the study. LEC, PHE, and LR analyzed the data and wrote the paper. LEC also completed the primary literature review and constructed all tables and figures in the manuscript.