[1] Columbia Univ, Irving Med Ctr, Irving Med Ctr, New York, NY 10032 USA
[2] NYU, Ronald O Perelman Dept Dermatol, Grossman Sch Med, New York, NY USA
[3] Univ Calif San Francisco, Dept Dermatol, 2340 Sutter St,N421, San Francisco, CA 94115 USA
[4] Univ Calif San Francisco, San Francisco Lib, San Francisco, CA 94143 USA
[5] London Sch Hyg & Trop Med, Fac Epidemiol & Populat Hlth, London, England
[6] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA USA