title: The application of new molecular methods in the investigation of a waterborne outbreak of norovirus in Denmark, 2012.
abstract: In December 2012, an outbreak of acute gastrointestinal illness occurred in a geographical distinct area in Denmark covering 368 households. A combined microbiological, epidemiological and environmental investigation was initiated to understand the outbreak magnitude, pathogen(s) and vehicle in order to control the outbreak. Norovirus GII.4 New Orleans 2009 variant was detected in 15 of 17 individual stool samples from 14 households. Norovirus genomic material from water samples was detected and quantified and sequencing of longer parts of the viral capsid region (>1000 nt) were applied to patient and water samples. All five purposely selected water samples tested positive for norovirus GII in levels up to 1.8×10(4) genomic units per 200 ml. Identical norovirus sequences were found in all 5 sequenced stool samples and 1 sequenced water sample, a second sequenced water sample showed 1 nt (<0.1%) difference. In a cohort study, including 256 participants, cases were defined as residents of the area experiencing diarrhoea or vomiting onset on 12-14 December 2012. We found an attack rate of 51%. Being a case was associated with drinking tap-water on 12-13 December (relative risk = 6.0, 95%CI: 1.6-22) and a dose-response relation for the mean glasses of tap-water consumed was observed. Environmental investigations suggested contamination from a sewage pipe to the drinking water due to fall in pressure during water supply system renovations. The combined microbiological, epidemiological and environmental investigations strongly indicates the outbreak was caused by norovirus contamination of the water supply system.
authors.affiliation: Department of Microbiological Diagnostics and Virology, Statens Serum Institut, Copenhagen, Denmark; European Programme of Public Health Microbiology (EUPHEM), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden.
authors.forename: Lieke B
authors.initials: LB
authors.lastname: van Alphen
authors.affiliation: Department of Infectious Disease Epidemiology, Statens Serum Institut, Copenhagen, Denmark; European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Dorléans
authors.affiliation: National Food Institute, Division of Food Microbiology, Danish Technical University (DTU), Lyngby, Denmark.
authors.forename: Anna Charlotte
authors.initials: AC
authors.lastname: Schultz
authors.affiliation: Department of Microbiological Diagnostics and Virology, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Jannik
authors.initials: J
authors.lastname: Fonager
authors.affiliation: Department of Infectious Disease Epidemiology, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Steen
authors.initials: S
authors.lastname: Ethelberg
authors.affiliation: Department of Microbiological Diagnostics and Virology, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Camilla
authors.initials: C
authors.lastname: Dalgaard
authors.affiliation: Danish Health and Medicines Authority, Public Health Medical Officers East, Denmark.
authors.forename: Marianne
authors.initials: M
authors.lastname: Adelhardt
authors.affiliation: Regional Clinical Microbiology Laboratory, Region Zealand, Denmark.
authors.forename: Jørgen H
authors.initials: JH
authors.lastname: Engberg
authors.affiliation: Department of Microbiological Diagnostics and Virology, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Thea Kølsen
authors.initials: TK
authors.lastname: Fischer
authors.affiliation: Department of Infectious Disease Epidemiology, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Sofie Gillesberg
authors.initials: SG
authors.lastname: Lassen
mesh_terms: D017250:Caliciviridae Infections / Q000453:epidemiology / Q000821:virology*; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D004196:Disease Outbreaks; D060766:Drinking Water / Q000821:virology*; D004784:Environmental Monitoring; D016679:Genome, Viral; D029322:Norovirus / Q000235:genetics* / Q000302:isolation & purification; D010802:Phylogeny; D018508:Water Purification; D014881:Water Supply
chemical_list: D036022:Capsid Proteins; D060766:Drinking Water