title: Use of sequential case-control studies to investigate a community Salmonella outbreak in Wales.
abstract: OBJECTIVE
  To establish the source of a community outbreak of Salmonella typhimurium definitive type 124.
  
  
  METHODS
  Two stage case-control study.
  
  
  METHODS
  Three districts in south east Wales.
  
  
  METHODS
  Cases of salmonella food poisoning and community controls.
  
  
  RESULTS
  An initial case-control study identified an association between illness and eating ham (odds ratio 4.50, 95% confidence intervals 1.10, 21.8) and also found a possible association between illness and food bought from delicatessen stores (odds ratio 5.03, 95% confidence intervals 1.01, 32.3). However, only after a second stage case-control study was a single common ham producer identified as the source (odds ratio 25.0, 95% confidence intervals 2.33, 1155).
  
  
  CONCLUSIONS
  Sequential case-control studies are an important and underused tool in the investigation of community outbreaks.
authors.affiliation: Public Health Laboratory Service Communicable Disease Surveillance Centre (Welsh Unit), Cardiff.
authors.forename: L J
authors.initials: LJ
authors.lastname: Llewellyn
authors.forename: M R
authors.initials: MR
authors.lastname: Evans
authors.forename: S R
authors.initials: SR
authors.lastname: Palmer
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008460:Meat / Q000382:microbiology*; D008875:Middle Aged; D012478:Salmonella Food Poisoning / Q000453:epidemiology / Q000382:microbiology*; D012486:Salmonella typhimurium; D013552:Swine; D014852:Wales / Q000453:epidemiology