[1] Univ Penn, Sch Med, Dept Pathol & Lab Med, Philadelphia, PA 19104 USA
[2] MCP Hahnemann Univ, St Christophers Hosp Children, Dept Pediat, Philadelphia, PA USA
[3] Wistar Inst Anat & Biol, Philadelphia, PA 19104 USA
[4] Wyeth Lederle Vaccines & Pediat, Malvern, PA USA
[5] Coulston Fdn, Alamogordo, NM USA
[6] Emory Univ, Rollins Sch Publ Hlth, Atlanta, GA 30322 USA
[7] Johns Hopkins Univ, Sch Med, Baltimore, MD USA
[8] Univ S Florida, Coll Med, Dept Med Microbiol & Immunol, Tampa, FL 33612 USA