title: Epidemiological survey and analysis on an outbreak of gastroenteritis due to water contamination.
abstract: OBJECTIVE
  To document the investigation and control of an outbreak of gastroenteritis in City G, South China, and provide a reference for preventing future outbreaks.
  
  
  METHODS
  An ambispective cohort study was designed. Attack rate (AR) and relative risks (RR) were calculated to identify the causes of gastroenteritis. Investigations using questionnaires included personal interviews with patients and doctors, reviews of medical records, laboratory examinations of fecal specimens and continuous hygiene monitoring of water samples from the waterworks.
  
  
  RESULTS
  Overall, 427/71534 (AR=5.97%) cases were identified between October 31 and November 12 2010. Geographic distribution was highly localized, with 80% of cases occurring in the areas supplied by waterworks-A. Consumption of water provided solely by waterworks-A was found to be associated with illness (RR=8.20, 95 CI%:6.12-10.99) compared with that from waterworks-B. Microbiological analyses confirmed the presence of Norovirus in six of eight fecal samples from symptomatic patients, two water samples from waterworks-A and two sewage samples. After taking effective measures, the hygienic indices of waterworks-A met health criteria again on November 9 and no cases were reported 3 days later.
  
  
  CONCLUSIONS
  The outbreak reported here was caused by drinking tap water contaminated with sewage at the source. Early identification of possible contamination sources and awareness of changes that might negatively impact water quality are important preventive measures to protect public health.
authors.affiliation: Guangzhou Center for Disease Control and Prevention, Guangdong, China. yangzc@gzcdc.org.cn
authors.forename: ZhiCong
authors.initials: Z
authors.lastname: Yang
authors.forename: XinWei
authors.initials: X
authors.lastname: Wu
authors.forename: TieGang
authors.initials: T
authors.lastname: Li
authors.forename: MeiXia
authors.initials: M
authors.lastname: Li
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhong
authors.forename: YuFei
authors.initials: Y
authors.lastname: Liu
authors.forename: Zhiai
authors.initials: Z
authors.lastname: Deng
authors.forename: Biao
authors.initials: B
authors.lastname: DI
authors.forename: Cong
authors.initials: C
authors.lastname: Huang
authors.forename: HuiYing
authors.initials: H
authors.lastname: Liang
authors.forename: Ming
authors.initials: M
authors.lastname: Wang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D005759:Gastroenteritis / Q000453:epidemiology* / Q000209:etiology; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D014876:Water Pollution / Q000009:adverse effects*; D055815:Young Adult