1. Division of Infectious Diseases, Department of Internal Medicine and Department of Molecular Microbiology and Pathogenesis, Washington University School of Medicine, St. Louis, Missouri 63110
2. Research Service, Albuquerque Veterans Administration Medical Center, Albuquerque, New Mexico 87108
3. Department of Molecular Genetics and Microbiology, University of New Mexico, Albuquerque, New Mexico 87131