1. Department of Basic Science and Craniofacial Biology,
2. Division of Diagnostics, Infectious Disease and Health Promotion, and
3. Department of Epidemiology and Health Promotion, New York University College of Dentistry, 345 East 24th Street, New York, NY 10010-4086, USA; and
4. Department of Epidemiology, School of Public Health, University of Alabama at Birmingham, Birmingham, AL 35294, USA