title: Transmission pathways for sporadic Shiga-toxin producing E. coli infections: A systematic review and meta-analysis.
abstract: BACKGROUND
  Shiga-toxin E. coli infections remain a public health concern because of the severity of the gastrointestinal illness and associated complications. Transmission pathways are typically elucidated from outbreaks, with foodborne transmission the primary source. However, most STEC cases are sporadic. This systematic review aimed to identify the most common pathways for sporadic STEC transmission and quantify their importance.
  
  
  METHODS
  We systematically reviewed epidemiological studies of sporadic (non-outbreak) STEC cases that investigated potential risk factors. Searches were run in Medline, EMBASE, and Scopus. Included studies needed to confirm STEC infection and investigate ≥20 cases.
  
  
  RESULTS
  31 studies were included, of which 25 were case-control or case-case studies. 62.5% found consumption of undercooked/raw meat associated with STEC infection while 70.4% found contact with animals or their environment a risk factor. Random-effects meta-analysis provided pooled odds ratios and population attributable fraction (PAF). The PAF was 19% for undercooked/raw meat, followed by person to person transmission at 15%. Contact with animals and visiting farm environments had PAFs of 14% and 12% respectively.
  
  
  CONCLUSIONS
  Out of potential sources for STEC exposure, undercooked meat and contact with animals and their environment were the most frequently found transmission routes. Decreasing the chances of acquiring the bacteria by these methods would additionally cut down on the other major transmission route, person-to-person spread.
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich NR4 7TJ, UK; NIHR Health Protection Research Unit in Gastrointestinal Infections, University of East Anglia, UK.
authors.forename: Erica
authors.initials: E
authors.lastname: Kintz
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: Julii
authors.initials: J
authors.lastname: Brainard
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich NR4 7TJ, UK; NIHR Health Protection Research Unit in Gastrointestinal Infections, University of East Anglia, UK.
authors.forename: Lee
authors.initials: L
authors.lastname: Hooper
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich NR4 7TJ, UK; NIHR Health Protection Research Unit in Gastrointestinal Infections, University of East Anglia, UK; Department of Environmental Health, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa. Electronic address: paul.hunter@uea.ac.uk.
authors.forename: Paul
authors.initials: P
authors.lastname: Hunter
mesh_terms: D000818:Animals; D000829:Animals, Domestic; D003296:Cooking; D003611:Dairy Products; D060766:Drinking Water; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000635:transmission*; D005506:Food Contamination; D006801:Humans; D008460:Meat; D054323:Shiga-Toxigenic Escherichia coli
chemical_list: D060766:Drinking Water
keywords: Epidemiology; Public health; Risk factors; Shiga-toxin producing E. coli