[1] Washington Univ, Sch Med, Dept Mol Microbiol, St Louis, MO 63110 USA
[2] Univ Washington, Sch Med, Dept Med, St Louis, MO USA
[3] Univ Washington, Sch Med, Dept Pathol, St Louis, MO USA
[4] Tufts Univ, Sch Vet Med, Dept Biomed Sci, Div Infect Dis, Boston, MA 02111 USA
[5] Tufts Univ, Sch Med, Dept Family Hlth & Community Med, Boston, MA 02111 USA