1. Department of Physical Medicine & Rehabilitation, Harvard Medical School, Boston, Massachusetts, USA.
2. Department of Laboratory Medicine & Pathology, Mayo Clinic, Rochester, Minnesota, USA.
3. Department of Pathology, Microbiology & Immunology and Vanderbilt University Medical Center, Nashville, Tennessee, USA.
4. Department of Biostatistics, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
5. Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA.