1. Department of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
2. Department of Biostatistics, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
3. Department of Epidemiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
4. Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
5. Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
6. Department of Medicine, University of Texas Health Science Center at Houston, Houston, TX 77030, USA.