1. Navy Environmental Health Center, Portsmouth, Virginia, USA;
2. Department of Defense Global Emerging Infections Surveillance and Response System, Silver Spring, Maryland, USA
3. Navy Environmental Health Center, Portsmouth, Virginia, USA;Preliminary findings were presented at the US Army Force Health Protection Conference, August 2003, Albuquerque, NM; the International Conference on Emerging Infectious Diseases, February 2004, Atlanta, GA; and the Navy Occupational Health and Preventive Medicine Workshop, March 2004, Norfolk, VA.