title: A waterborne outbreak with a single clone of Campylobacter jejuni in the Danish town of Køge in May 2010.
abstract: BACKGROUND
  In Denmark, large-scale waterborne outbreaks are rare. This report describes the investigation of an outbreak that occurred in the town of Køge in May 2010.
  
  
  METHODS
  The epidemiological investigation consisted of hypothesis generating telephone interviews, followed by a cohort study among approximately 20,000 residents using an online questionnaire. Odds ratios were calculated for exposures including the number of glasses of tap water consumed. Geographical spreading was assessed using a geographical information system. The microbiological investigation included cultures of stool samples and flagellin-typing. In the environmental investigation, water samples were tested for Escherichia coli and coliform counts and for DNA of Campylobacter, Enterococcus, and Bacteroides. During the outbreak investigation a water boiling order was enforced, as tap water was considered a potential source.
  
  
  RESULTS
  Of 45 patients with laboratory confirmed Campylobacter infection in the municipality of Køge in May, 43 lived in the area covered by the central water supply. Of 61 patients with laboratory confirmed Campylobacter jejuni by 8 June, 50 shared a common flagellin gene type--flaA type 36 (82%). The epidemic curve from the cohort study showed a wave of diarrhoea onset from 14 to 20 May (n = 176). Among these patients, the development of diarrhoea was associated with drinking tap water with a dose-response pattern (linear increase by 2 glasses: odds ratio 1.40, 95% confidence interval 1.16-1.70). No bacterial DNA was found in water samples.
  
  
  CONCLUSIONS
  These findings indicated a point source contamination of tap water with a single clone of C. jejuni which likely occurred on 12-13 May. The water boiling order was lifted on 18 June.
authors.affiliation: European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control, Stockholm, Sweden. gub@ssi.dk
authors.forename: Sophie-Madeleine
authors.initials: SM
authors.lastname: Gubbels
authors.forename: Katrin G
authors.initials: KG
authors.lastname: Kuhn
authors.forename: Jonas T
authors.initials: JT
authors.lastname: Larsson
authors.forename: Marianne
authors.initials: M
authors.lastname: Adelhardt
authors.forename: Jørgen
authors.initials: J
authors.lastname: Engberg
authors.forename: Pernille
authors.initials: P
authors.lastname: Ingildsen
authors.forename: Line Wilchen
authors.initials: LW
authors.lastname: Hollesen
authors.forename: Steen
authors.initials: S
authors.lastname: Muchitsch
authors.forename: Kåre
authors.initials: K
authors.lastname: Mølbak
authors.forename: Steen
authors.initials: S
authors.lastname: Ethelberg
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002169:Campylobacter Infections / Q000453:epidemiology* / Q000382:microbiology; D016123:Campylobacter jejuni / Q000235:genetics / Q000302:isolation & purification*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D004196:Disease Outbreaks; D060766:Drinking Water / Q000382:microbiology*; D005260:Female; D005408:Flagellin / Q000235:genetics; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio
chemical_list: D060766:Drinking Water; D005408:Flagellin; C067138:flaA protein, bacteria