[1] London Sch Hyg & Trop Med, Dept Social & Environm Hlth Res, London WC1H 9SH, England
[2] SUNY Albany, Dept Environm Hlth Sci, Sch Publ Hlth, New York, NY 12114 USA
[3] SUNY Albany, Dept Epidemiol & Biostat, Sch Publ Hlth, New York, NY 12114 USA
[4] Ctr Dis Control & Prevent, Natl Ctr Environm Hlth, Atlanta, GA 30341 USA