[1] JOHNS HOPKINS UNIV,SCH MED,DEPT MED,BALTIMORE,MD 21205
[2] FRANCIS SCOTT KEY MED CTR,DEPT MED,BALTIMORE,MD 21224
[3] UNIV MARYLAND,SCH MED,DIV GEOG MED,CTR VACCINE DEV,BALTIMORE,MD 21201
[4] HARVARD UNIV,SCH MED,DEPT MICROBIOL & MOLEC GENET,BOSTON,MA 02115