1. Section of Infectious Diseases, Department of Medicine, University of Chicago, Chicago, Illinois.
2. Section of Infectious Diseases, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois.
3. Abbott Laboratories, Abbott Park, Illinois.
4. Howard Brown Health Center, Chicago, Illinois.
5. Section of Infectious Diseases, Department of Medicine, Rush University, Chicago, Illinois.
6. Department of Immunology and Microbiology, Rush University, Chicago, Illinois.