[1] Univ Southern Calif, Keck Sch Med, Dept Populat & Publ Hlth Sci, Los Angeles, CA 90007 USA
[2] Univ Southern Calif, Keck Sch Med, Dept Pediat, Los Angeles, CA 90007 USA
[3] LAC USC Med Ctr, Dept Med, Div Hosp Med, Los Angeles, CA USA
[4] Univ Calif Irvine, Dept Epidemiol & Biostat, Irvine, CA USA
[5] Univ Southern Calif, Keck Sch Med, Dept Dermatol, Los Angeles, CA 90007 USA
[6] Univ Southern Calif, Keck Sch Med, Dept Populat & Publ Hlth Sci, 2001 N Soto St,3rd Floor,Room 312-30, Los Angeles, CA 90032 USA