title: Giardia cysts in sewage influent in Bergen, Norway 15-23 months after an extensive waterborne outbreak of giardiasis.
abstract: OBJECTIVE
  In autumn/winter 2004, a large outbreak of waterborne giardiasis occurred in Bergen, Norway. Over 1 year later, the concentrations and genotypes of Giardia cysts occurring in sewage influent were studied to investigate the impact of the outbreak event on Giardia infections in the community.
  
  
  RESULTS
  Sewage influent samples from four sewage treatment works (STW) serving Bergen were analysed for Giardia cysts on four occasions between 15 and 23 months after the outbreak. Cysts genotypes were investigated at one to three genes. Data from influent analysis from one of the STW before the outbreak, and from patient faecal samples analysed during the outbreak, provided baseline comparative data. Relatively high concentrations of Giardia cysts of diverse genotypes, both from Assemblages A and B, were detected at all STW.
  
  
  CONCLUSIONS
  Comparison of data suggests that although Giardia cyst concentrations in sewage influent returned to pre-outbreak levels within 18 months after the outbreak peak, the genetic composition of the isolates remained significantly influenced by the Assemblage B isolate associated with the outbreak.
  
  
  CONCLUSIONS
  Genotypes associated with an extensive outbreak of giardiasis continued to occur in Giardia infections in Bergen's population many months after the outbreak was considered to be over.
authors.affiliation: Parasitology Laboratory, Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, Oslo, Norway. lucy.robertson@veths.no
authors.forename: L J
authors.initials: LJ
authors.lastname: Robertson
authors.forename: T
authors.initials: T
authors.lastname: Forberg
authors.forename: B K
authors.initials: BK
authors.lastname: Gjerde
mesh_terms: D000818:Animals; D004196:Disease Outbreaks; D017125:Genes, Protozoan; D005838:Genotype; D005872:Giardia / Q000302:isolation & purification*; D005873:Giardiasis / Q000453:epidemiology*; D006801:Humans; D009664:Norway / Q000453:epidemiology; D033661:Oocysts; D010270:Parasite Egg Count; D016133:Polymerase Chain Reaction; D012621:Seasons; D012722:Sewage / Q000469:parasitology*; D013995:Time; D014871:Water Microbiology
chemical_list: D012722:Sewage