1. J. W. Mellors, Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA; Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA; and Veterans Affairs Medical Center, Pittsburgh, PA 15240, USA.
2. C. R. Rinaldo Jr., Department of Pathology, School of Medicine, and Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA.
3. P. Gupta, Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA.
4. R. M. White and J. A. Todd, Chiron Corporation, Emeryville, CA 94608, USA.
5. L. A. Kingsley, Department of Infectious Diseases and Microbiology and Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA.