[1] Vet Affairs Med Ctr, Dept Med, Houston, TX 77030 USA
[2] Baylor Coll Med, Dept Med, Houston, TX 77030 USA
[3] Baylor Coll Med, Dept Mol Virol & Microbiol, Houston, TX 77030 USA
[4] Hokkaido Univ, Sch Med, Dept Endoscopy, Sapporo, Hokkaido 060, Japan
[5] Sungkyunkwan Univ, Samsung Med Ctr, Dept Med, Seoul, South Korea