[1] Emory Univ, Sch Med, Dept Pediat, Atlanta, GA USA
[2] Univ Calif San Francisco, Sch Med, San Francisco, CA USA
[3] Ctr Dis Control & Prevent, Atlanta, GA USA
[4] Univ Penn, Childrens Hosp Philadelphia, Philadelphia, PA 19104 USA
[5] Univ Penn, Perelman Sch Med, Philadelphia, PA 19104 USA
[6] Univ Utah, Salt Lake City, UT USA