1. Armed Forces Health Surveillance Center, Silver Spring, Maryland, USA
2. Naval Health Research Center, San Diego, California, USA
3. Mayo Clinic, Division of General Internal Medicine, Rochester, Minnesota, USA
4. Oak Ridge Institute for Science and Education, Postgraduate Research Participation Program, U.S. Army Public Health Command, Aberdeen Proving Ground, Aberdeen, Maryland, USA
5. International STD, Respiratory, and Biothreat Research Laboratory, Division of Infectious Diseases, Johns Hopkins University, Baltimore, Maryland, USA