1. Department of Molecular Genetics and Biochemistry, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
2. Children's Memorial Hospital, Northwestern University, Evanston, Illinois 60201.
3. Department of Pathology, Stanford University School of Medicine, Stanford, California 94304.
4. Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
5. Division of Infectious Diseases, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
6. Department of Infectious Diseases and Microbiology, Graduate School of Public Health, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.