[1] Santa Clara Valley Med Ctr, Fruitdale, CA USA
[2] McMaster Univ, Internal Med, Hamilton, ON, Canada
[3] Tufts Univ, Sch Med, Boston, MA USA
[4] Brown Univ, Sch Publ Hlth, Providence, RI 02912 USA
[5] Stanford Univ, Sch Med, Div Gastroenterol & Hepatol, Stanford, CA 94305 USA