1. Biostatistics Research Branch, National Institute of Allergy and Infectious Diseases, 6700B Rockledge Drive, Bethesda, MD 20892–7630, USA.
2. Division of Microbiology and Infectious Diseases, National Institute of Allergy and Infectious Diseases, 6610 Rockledge Drive, Bethesda, MD 20892–6604, USA.
3. Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA 30333, USA.
4. Battelle, 505 King Avenue, Columbus, OH 43201, USA.
5. Blair & Co., Greenwich, CT 06830, USA.