[1] Univ Penn, Perelman Sch Med, Div Infect Dis, Philadelphia, PA 19104 USA
[2] Univ Penn, Perelman Sch Med, Dept Pediat, Philadelphia, PA 19104 USA
[3] Univ Penn, Perelman Sch Med, Dept Biostat & Epidemiol, Philadelphia, PA 19104 USA
[4] Childrens Hosp Philadelphia, Philadelphia, PA 19104 USA
[5] Childrens Hosp Philadelphia, Ctr Pediat Clin Effectiveness Res, Philadelphia, PA 19104 USA