[1] Univ Birmingham, Dept Populat Sci & Humanities, Birmingham, W Midlands, England
[2] Univ Sierra Leone, Coll Med & Allied Hlth Sci, Freetown, Sierra Leone
[3] Johns Hopkins Univ, Sch Med, Dept Anesthesiol & Crit Care Med, Baltimore, MD 21287 USA
[4] Johns Hopkins Univ, Sch Med, Dept Surg, Baltimore, MD 21287 USA
[5] Johns Hopkins Univ Hosp, Dept Med, Baltimore, MD 21287 USA
[6] Univ Birmingham, Dept Publ Hlth Epidemiol & Biostat, Birmingham, W Midlands, England
[7] Univ Sierra Leone, Connaught Hosp, Dept Surg, Freetown, Sierra Leone