[1] Vet Affairs Palo Alto Hlth Care Syst, Populat Hlth Program, Off Publ Hlth, Palo Alto, CA 94304 USA
[2] Vet Affairs Palo Alto Hlth Care Syst, Dept Med, Div Gastroenterol & Hepatol, Palo Alto, CA 94304 USA
[3] Vet Affairs Palo Alto Hlth Care Syst, Dept Med, Palo Alto, CA 94304 USA
[4] Stanford Univ, Dept Med, Div Gastroenterol & Hepatol, Stanford, CA 94305 USA