[1] MONTREAL GEN HOSP,DEPT EPIDEMIOL & BIOSTAT,MONTREAL H3G 1A4,QUEBEC,CANADA
[2] MONTREAL GEN HOSP,DEPT MED,MONTREAL H3G 1A4,QUEBEC,CANADA
[3] MCGILL UNIV,MONTREAL H3A 2T5,QUEBEC,CANADA
[4] UNIV SASKATCHEWAN,DEPT MED,SASKATOON S7N 0W0,SASKATCHEWAN,CANADA
[5] UNIV SASKATCHEWAN,DEPT COMMUNITY HLTH & EPIDEMIOL,SASKATOON S7N 0W0,SASKATCHEWAN,CANADA
[6] YALE UNIV,SCH MED,NEW HAVEN,CT 06510
[7] SASKATCHEWAN DEPT HLTH,LAB & DIS CONTROL SERV BRANCH,HE ROBERTSON LAB,REGINA,SASKATCHEWAN,CANADA
[8] OREGON HLTH SCI UNIV,DEPT MED,PORTLAND,OR 97201
[9] OREGON HLTH SCI UNIV,DEPT PHYSIOL,PORTLAND,OR 97201