[1] Dalhousie Univ, Interdisciplinary PhD Program, Halifax, NS, Canada
[2] Dalhousie Univ, Dept Obstet & Gynaecol & Paediat, Halifax, NS, Canada
[3] Hlth Canada, Hlth Environm & Consumer Safety Branch, Ottawa, ON K1A 0L2, Canada
[4] Dalhousie Univ, Dept Community Hlth & Epidemiol, Halifax, NS, Canada
[5] McGill Univ, Dept Epidemiol & Biostat, Montreal, PQ, Canada
[6] Dalhousie Univ, Dept Microbiol & Immunol, Halifax, NS, Canada