[1] British Columbia Ctr Dis Control, Vancouver, BC, Canada
[2] London Sch Hyg & Trop Med, London WC1, England
[3] Kent State Univ, Kent, OH 44242 USA
[4] Inst Veille Sanit, Paris, France
[5] Inst Salud Carlos III, Madrid, Spain
[6] Hlth Canada, Ottawa, ON K1A 0L2, Canada
[7] Environm Canada, Ottawa, ON K1A 0H3, Canada