1. University of Pennsylvania School of Medicine, Department of Microbiology, 3610 Hamilton Walk, Philadelphia, Pennsylvania 19104-6076
2. University of Florida College of Medicine, Department of Medicine, 1600 SW Archer Road, Gainesville, Florida 32610
3. Department of Medicine, A424, Medical Research Building, Philadelphia VA Medical Center, University and Woodland Avenue, Philadelphia, Pennsylvania 19104
4. Department of Civil Engineering, University of Glasgow, Glasgow G12 8LT, United Kingdom