[1] Johns Hopkins Univ, Sch Med, Dept Emergency Med, Baltimore, MD USA
[2] Johns Hopkins Univ, Bloomberg Sch Publ Hlth, Dept Hlth Policy & Management, Baltimore, MD USA
[3] Johns Hopkins Univ, Bloomberg Sch Publ Hlth, Dept Epidemiol, Baltimore, MD USA
[4] Johns Hopkins Univ, Sch Med, Dept Med, Baltimore, MD 21205 USA