[1] Univ Memphis, Sch Publ Hlth, Div Epidemiol, Memphis, TN 38152 USA
[2] Univ Tennessee, Hlth Sci Ctr, Dept Pediat, 50 N Dunlap St, Memphis, TN 38103 USA
[3] Vanderbilt Univ, Sch Med, Dept Pediat, Nashville, TN 37212 USA
[4] Vanderbilt Univ, Sch Med, Dept Hlth Policy, Nashville, TN 37212 USA
[5] Vanderbilt Univ, Sch Med, Dept Emergency Med, Nashville, TN 37212 USA
[6] Emory Univ, Sch Med, Ctr Dis Control & Prevent, Atlanta, GA USA
[7] Emory Univ, Sch Med, Dept Pediat, Atlanta, GA USA
[8] Emory Univ, Sch Med, Dept Med, Atlanta, GA USA
[9] Univ Utah, Hlth Sci Ctr, Dept Pediat, Salt Lake City, UT USA
[10] Northwestern Univ, Dept Med, Feinberg Sch Med, Chicago, IL 60611 USA