[1] Univ London Imperial Coll Sci Technol & Med, Med Res Council, Hlth Protect Agcy, Ctr Environm & Hlth,Dept Epidemiol & Biostat,Sch, London W2 1PG, England
[2] Harvard Univ, Sch Publ Hlth, Dept Global Hlth & Populat, Boston, MA 02115 USA
[3] Harvard Univ, Sch Publ Hlth, Dept Environm Hlth, Boston, MA 02115 USA
[4] Univ Ghana, Environm Sci Program, Legon, Ghana
[5] Univ Ghana, Dept Phys, Legon, Ghana
[6] Univ Ghana, Dept Geog & Resource Dev, Legon, Ghana