[1] Brown Univ, Mem Hosp Rhode Isl, Div Infect Dis, Pawtucket, RI 02860 USA
[2] Brown Univ, Sch Med, Div Infect Dis, Providence, RI 02912 USA
[3] Xoma Inc, Berkeley, CA USA
[4] Free Univ Brussels, Erasme Hosp, B-1050 Brussels, Belgium
[5] Univ Iowa, Dept Prevent Med & Environm Hlth, Iowa City, IA USA