[1] MASSACHUSETTS GEN HOSP, INFECT DIS UNIT, BOSTON, MA 02114 USA
[2] HARVARD UNIV, SCH MED, DEPT MICROBIOL & MOLEC GENET, BOSTON, MA 02115 USA
[3] NEW ENGLAND MED CTR, DIV GEOG MED & INFECT DIS, BOSTON, MA 02111 USA
[4] TUFTS UNIV, SCH MED, BOSTON, MA 02111 USA