[1] Univ N Carolina, Dept Epidemiol, Chapel Hill, NC 27599 USA
[2] Univ Calif San Francisco, Sch Med, San Francisco, CA 94143 USA
[3] Johns Hopkins Univ, Sch Med, Baltimore, MD USA
[4] Univ Calif San Diego, Sch Med, San Diego, CA 92103 USA
[5] Univ Washington, Sch Med, Seattle, WA USA
[6] Univ N Carolina, Sch Med, Chapel Hill, NC 27599 USA
[7] Univ Alabama Birmingham, Sch Med, Birmingham, AL USA