1. Yale School of Public Health, Yale University School of Medicine, New Haven, Connecticut, USA
2. Departments of Medicine and Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA
3. Yale University School of Nursing, New Haven, Connecticut, USA
4. Department of Molecular Biophysics and Biochemistry and the W.M. Keck Foundation, Biotechnology Resource Laboratory, Yale University, New Haven, Connecticut, USA