title: Increased risk of A(H1N1)pdm09 influenza infection in UK pig industry workers compared to a general population cohort.
abstract: Pigs are mixing vessels for influenza viral reassortment, but the extent of influenza transmission between swine and humans is not well understood.
  
  
  
  To assess whether occupational exposure to pigs is a risk factor for human infection with human and swine-adapted influenza viruses.
  
  
  
  UK pig industry workers were frequency-matched on age, region, sampling month, and gender with a community-based comparison group from the Flu Watch study. HI assays quantified antibodies for swine and human A(H1) and A(H3) influenza viruses (titres ≥ 40 considered seropositive and indicative of infection). Virus-specific associations between seropositivity and occupational pig exposure were examined using multivariable regression models adjusted for vaccination. Pigs on the same farms were also tested for seropositivity.
  
  
  
  Forty-two percent of pigs were seropositive to A(H1N1)pdm09. Pig industry workers showed evidence of increased odds of A(H1N1)pdm09 seropositivity compared to the comparison group, albeit with wide confidence intervals (CIs), adjusted odds ratio after accounting for possible cross-reactivity with other swine A(H1) viruses (aOR) 25·3, 95% CI (1·4-536·3), P = 0·028.
  
  
  
  The results indicate that A(H1N1)pdm09 virus was common in UK pigs during the pandemic and subsequent period of human A(H1N1)pdm09 circulation, and occupational exposure to pigs was a risk factor for human infection. Influenza immunisation of pig industry workers may reduce transmission and the potential for virus reassortment.
authors.affiliation: Department of Infectious Disease Informatics, Farr Institute of Health Informatics Research, University College London, London, UK.|Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK.
authors.forename: Ellen
authors.initials: E
authors.lastname: Fragaszy
authors.affiliation: Department of Infectious Disease Informatics, Farr Institute of Health Informatics Research, University College London, London, UK.|Immunisation Department, Public Health England, London, UK.
authors.forename: David A
authors.initials: DA
authors.lastname: Ishola
authors.affiliation: Animal and Plant Health Agency (formerly Animal Health and Veterinary Laboratories Agency), Weybridge, UK.
authors.forename: Ian H
authors.initials: IH
authors.lastname: Brown
authors.affiliation: Health Protection and Influenza Research Group, Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK.
authors.forename: Joanne
authors.initials: J
authors.lastname: Enstone
authors.affiliation: Health Protection and Influenza Research Group, Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK.
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Nguyen-Van-Tam
authors.affiliation: Animal and Plant Health Agency (formerly Animal Health and Veterinary Laboratories Agency), Weybridge, UK.
authors.forename: Robin
authors.initials: R
authors.lastname: Simons
authors.affiliation: Disease Dynamics Unit, Department of Veterinary Medicine, University of Cambridge, Cambridge, UK.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Tucker
authors.affiliation: Royal Veterinary College, North Mymms, UK.|ILRI: International Livestock Research Institute, Addis Ababa, Ethiopia.
authors.forename: Barbara
authors.initials: B
authors.lastname: Wieland
authors.affiliation: Animal and Plant Health Agency (formerly Animal Health and Veterinary Laboratories Agency), Weybridge, UK.
authors.forename: Susanna M
authors.initials: SM
authors.lastname: Williamson
authors.affiliation: Department of Infectious Disease Informatics, Farr Institute of Health Informatics Research, University College London, London, UK.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Hayward
authors.affiliation: Disease Dynamics Unit, Department of Veterinary Medicine, University of Cambridge, Cambridge, UK.
authors.forename: James L N
authors.initials: JL
authors.lastname: Wood
mesh_terms: D000328:Adult; D000368:Aged; D000822:Animal Husbandry; D000818:Animals; D015331:Cohort Studies; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D007251:Influenza, Human / Q000635:transmission / Q000821:virology*; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure / Q000706:statistics & numerical data; D009976:Orthomyxoviridae Infections / Q000635:transmission / Q000662:veterinary* / Q000821:virology*; D013552:Swine; D013553:Swine Diseases / Q000821:virology*; D006113:United Kingdom; D000078329:Workforce; D055815:Young Adult
keywords: Humans; influenza; occupational exposure; serology; swine; zoonoses