Increased risk of A(H1N1)pdm09 influenza infection in UK pig industry workers compared to a general population cohort

the Flu Watch Group, the Combating Swine Influenza (COSI) Consortium

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    19 Citations (Scopus)


    Background: Pigs are mixing vessels for influenza viral reassortment, but the extent of influenza transmission between swine and humans is not well understood. Objectives: To assess whether occupational exposure to pigs is a risk factor for human infection with human and swine-adapted influenza viruses. Methods: 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. Results: 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. Conclusion: 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.

    Original languageEnglish
    Pages (from-to)291-300
    Number of pages10
    JournalInfluenza and other Respiratory Viruses
    Issue number4
    Publication statusPublished - 1 Jul 2016

    Bibliographical note

    Funding Information:
    We thank Martina Velasova and Pablo Alarcon (RVC) for their support in recruiting pig farmers; Joanne Savage (UCL) for help with data and sample collection from pig veterinarians; Stephen Essen and Alex Holland at (AHVLA) for technical support; all the pig veterinarians, farm workers, Flu Watch participants and farms which participated in the study; the Pig Veterinary Society for assistance in recruiting pig veterinarians; and the National Reference Laboratory, Respiratory Virus Unit, Public Health England (Colindale, London) for help with sample processing.

    Publisher Copyright:
    © 2015 The Authors. Influenza and Other Respiratory Viruses Published by John Wiley & Sons Ltd.


    • Humans
    • influenza
    • occupational exposure
    • serology
    • swine
    • zoonoses


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