[1] Univ Penn, Perelman Sch Med, Dept Med, Philadelphia, PA 19104 USA
[2] Univ Penn, Dept Med, Perelman Sch Med, Pulm Allergy & Crit Care Div, Philadelphia, PA 19104 USA
[3] Univ Penn, Dept Emergency Med, Perelman Sch Med, Philadelphia, PA 19104 USA
[4] Univ Penn, Ctr Clin Epidemiol & Biostat, Perelman Sch Med, Philadelphia, PA 19104 USA
[5] Georgetown Univ, Sch Med, Dept Emergency Med, Medstar Washington Hosp Ctr, Washington, DC USA
[6] Univ Penn Hlth Syst, Philadelphia, PA USA
[7] Univ Penn, Wharton Sch, Philadelphia, PA 19104 USA