[1] Univ Penn, Sch Med, Dept Pathol & Lab Med, Philadelphia, PA 19104 USA
[2] Univ Penn, Sch Med, Dept Hosp Epidemiol & Infect Control, Philadelphia, PA 19104 USA
[3] Univ Penn, Sch Med, Dept Med, Div Infect Dis, Philadelphia, PA 19104 USA
[4] Univ Penn, Sch Med, Ctr Clin Epidemiol & Biostat, Dept Biostat & Epidemiol, Philadelphia, PA 19104 USA