[1] Univ Quebec, Hop St Sacrement, Ctr Hosp Affilie, Unite Rech Sante Populat, Ste Foy, PQ G1S 4L8, Canada
[2] Univ Laval, Dept Social & Prevent Med, Quebec City, PQ G1K 7P4, Canada
[3] Univ Quebec, Ctr Hosp, Unite Rech Sante Publ & Sante Environm, Ste Foy, PQ G1V 2M3, Canada
[4] Imperial Coll, Dept Infect Dis Epidemiol, London, England