[1] Vet Affairs Med Ctr, Med Serv, Minneapolis, MN 55417 USA
[2] Univ Minnesota, Dept Med, Minneapolis, MN 55455 USA
[3] WHO, Int Escherichia & Klebsiella Ctr, Copenhagen, Denmark
[4] Vet Adm Med Ctr, Med Serv, Buffalo, NY 14215 USA
[5] SUNY Buffalo, Dept Med, Buffalo, NY 14260 USA
[6] Univ Utrecht, Fac Vet Med, Inst Infect Dis & Immunol, Dept Bacteriol, Utrecht, Netherlands