title: An outbreak of norovirus caused by consumption of oysters from geographically dispersed harvest sites, British Columbia, Canada, 2004.
abstract: OBJECTIVE
  In January 2004, an increase in gastrointestinal illness following oyster consumption was reported in British Columbia. An investigation was initiated to explore the association between norovirus infection and consumption of British Columbia oysters and to identify the source of oyster contamination.
  
  
  METHODS
  The outbreak investigation included active surveillance for human cases, two cohort studies, trace-back of oysters, and laboratory testing of oysters and human stools.
  
  
  RESULTS
  Enhanced surveillance identified 26 confirmed and 53 clinical cases over 3 months. Oyster consumption was associated with illness in one cohort and suggestive in the other. Oysters were traced to 14 geographically dispersed harvest sites, 18 suppliers, and 45 points of purchase. Norovirus BCCDC03-028 (genotype I.2) was detected in 50% of human specimens. Experimental methods detected norovirus in 12 oyster samples. Sequencing identified mixed clonal patterns in the oysters with one direct sequence match between an oyster sample and the associated human specimen.
  
  
  CONCLUSIONS
  The consumption of raw oysters led to norovirus infection. The source of oyster contamination remained unidentified. The geographical dispersion of implicated harvest sites was unusual.
  
  
  CONCLUSIONS
  This outbreak is unlike most shellfish outbreaks that can be traced back to a common source and challenges conventional thinking that all oyster-related norovirus outbreaks of are a result of point source contamination.
authors: Canadian Field Epidemiology Program, Public Health Agency of Canada, Ottawa, ON, Canada. samara.david@bccdc.ca
authors: Samara T
authors: ST
authors: David
authors: Lorraine
authors: L
authors: McIntyre
authors: Laura
authors: L
authors: MacDougall
authors: Deirdre
authors: D
authors: Kelly
authors: Sing
authors: S
authors: Liem
authors: Klaus
authors: K
authors: Schallié
authors: Alan
authors: A
authors: McNabb
authors: Alain
authors: A
authors: Houde
authors: Peter
authors: P
authors: Mueller
authors: Pierre
authors: P
authors: Ward
authors: Yvon-Louis
authors: YL
authors: Trottier
authors: Julie
authors: J
authors: Brassard
mesh_terms: D000818:Animals; D001955:British Columbia / Q000453:epidemiology; D017250:Caliciviridae Infections / Q000453:epidemiology* / Q000821:virology; D004196:Disease Outbreaks; D005243:Feces / Q000821:virology; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D005759:Gastroenteritis / Q000453:epidemiology* / Q000821:virology; D006801:Humans; D029322:Norovirus / Q000145:classification / Q000302:isolation & purification; D010125:Ostreidae / Q000821:virology*; D018571:Sentinel Surveillance; D012758:Shellfish / Q000821:virology*; D014871:Water Microbiology