1. Travelers' Health Branch, Division of Global Migration and Quarantine, Centers for Disease Control and Prevention, Atlanta, Georgia.
2. Poxvirus and Rabies Branch, Division of High-Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia.
3. Department of Quantitative Health Sciences, University of Massachusetts Medical School, Worcester, Massachusetts.
4. Center for Health Quality, Outcomes and Economic Research, Bedford VA Medical Center, Bedford, Massachusetts.
5. Division of Infectious Diseases, Massachusetts General Hospital, Boston, Massachusetts.
6. Harvard Medical School, Boston, Massachusetts.