[1] MED COLL PENN, DEPT MICROBIOL IMMUNOL, PHILADELPHIA, PA 19129 USA
[2] ST CHRISTOPHERS HOSP CHILDREN, PHILADELPHIA, PA 19133 USA
[3] TEMPLE UNIV, HLTH SCI CTR, SCH MED, PHILADELPHIA, PA 19140 USA
[4] UNIV WASHINGTON, CHILDRENS ORTHOPED HOSP & MED CTR, SEATTLE, WA 98105 USA