[1] Univ Texas Hlth Ctr, CPIDC, Tyler, TX 75708 USA
[2] Univ Texas Hlth Ctr, Dept Microbiol & Immunol, Tyler, TX 75708 USA
[3] Univ Texas Hlth Ctr, Dept Med, Tyler, TX 75708 USA
[4] Univ N Texas, Hlth Sci Ctr, Dept Internal Med, Ft Worth, TX 76107 USA
[5] Univ Oxford, Nuffield Dept Clin Med, Oxford, England
[6] John Radcliffe Hosp, Oxford OX3 9DU, England