Population-based Surveillance for Zoonotic Influenza A
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Population-based Surveillance for Zoonotic Influenza A in Agricultural Workers. Abstract*. Acknowledgements. Conclusion. Results. Materials & Methods. Introduction. Less than 20 enrollees 21 – 35 enrollees 36 or more enrollees.

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Population-based Surveillance for Zoonotic Influenza A

in Agricultural Workers





Materials & Methods


  • Less than 20 enrollees

  • 21 – 35 enrollees

  • 36 or more enrollees

Gregory C. Gray, MD, MPH,1 Troy McCarthy,1 Ana W. Capuano, MPS, 1 Charles F. Lynch, MD, PhD,2 Debbie A. Wellman,1 Kelly A. Lesher,1 Sharon F. Setterquist, MT(ASCP),1 Norma J. Miller,1 Patricia A P Gillette,MPH,2 Christopher W. Olsen, DVM, PhD,3 Alexander I. Klimov, PhD,4

Michael C. Alavanja, PhD,5 and Jackie M. Katz, PhD6

Background - Swine may play an important role in cross-species influenza transmission and the genesis of novel influenza strains. We prospectively studied swine workers for serological evidence of zoonotic influenza infection.

Methods - Using data from the Agricultural Health Study (AHS), we identified, screened, and enrolled 803 rural Iowans from 29 counties in a 2-year prospective zoonotic influenza transmission study. Enrollment sera were studied with hemagglutination inhibition assays against two swine and one human influenza viral strains. Demographic and occupational risk factors were studied for associations with antibodies against swine H1N1 and H1N2 viruses using a multivariate proportional odds model at enrollment (AHS and Non-AHS) and follow-up (AHS only).

Results - Among the 803 subjects, 707 worked in swine production (AHS-E), 80 reported no previous swine exposure (AHS-NE) and 15 were excluded because of reported accidental self-injection with swine vaccine. Data and sera from 79 non-AHS control (N-AHS) subjects from a parallel study were used as a reference. (71%) of the 80 AHS-NE live in the same household (mostly wives) of AHS-E. Multivariate models controlled for human influenza viruses, flu shot, age, and/or gender. At enrollment, the AHS-E (>10 or ≤10 years of exposure)and the AHS-NE had markedly elevated adjusted odds of increased antibody titers against swine H1N1 (OR, 95%CI= 55.6, 13.1-236.1;51.3,11.1-236.5; 28.2, 6.1-130.1) and swine H1N2 (OR, 95%CI= 13.5, 6.1-29.8; 13,5.1-33; 6.9, 2.8-17.1) compared to the N-AHS.

Conclusion - These data suggest that swine influenza viral infections are common among swine workers and their non-exposed-to-swine spouses. Agriculture workers should be given special attention in influenza surveillance strategies and in planning for influenza pandemics.

*Abstract revised

1Center for Emerging Infectious Diseases, Dept. of Epidemiology, University of Iowa College of Public Health, Iowa City, IA; 2Department of Epidemiology, University of Iowa College of Public Health, Iowa City, IA; 3Department of Pathobiological Sciences, University of Wisconsin-Madison, Madison, WI; 4Strain Surveillance Section, Influenza Branch, Centers for Disease Control and Prevention, Atlanta, GA; 5National Cancer Institute, Bethesda, MD; 6Immunology and Viral Pathogenesis Section, Centers for Disease Control and Prevention, Atlanta, GA

To validate serological outcomes, culture and molecular studies will be performed on gargle and swab specimens to identify influenza and specific hemagglutinin types.

  • Human-to-swine and swine-to-human influenza transmission have been well-documented.

  • Olsen et. al. found that 23% of 74 swine farm workers had serologic evidence of emergent swine influenza infection as compared to <1% of urban controls (Emerg Infect Dis 2002;8:814-9).

  • Myers et. al. found farmers, meat processing workers, and veterinarian workers all to have higher odds of elevated antibodies against swine H1N1 and swine H1N2 influenza viruses compared to nonexposed controls (Clin Infect Dis,2006;42:14-20).

  • Many of the non-exposed subjects were spouses of the exposed, and although they reported little swine exposure, they had lived on a swine farm (Table 2).

  • Odds for having elevated antibodies against swine influenza viruses were high for the exposed and their non-exposed spouses compared to University of Iowa non-exposed controls (Table 3).

  • These data suggest that swine workers are at increased risk of swine influenza virus infections.

  • Swine worker spouses may also be at increased risk of infection through indirect swine viruses.

  • Agriculture workers should be given special attention in influenza surveillance strategies and in planning for influenza pandemics.

  • We used data from the 90,000-person Agricultural Health Study to identify 707 study subjects who were occupationally exposed to swine and/or poultry, and a gender and age-group matched group of 80 control subjects without such exposures.

  • Upon enrollment, and after 12 and 24 months of follow-up, participants are asked to complete a questionnaire and to donate sera (589 AHS-E and 69 AHS-NE).

  • During the 2 years of follow-up, if a participant develops signs and symptoms of an influenza-like illness, they complete a questionnaire, provide a gargle sample and a nasal swab within 48 hours of symptom development, and ship the questionnaire and gargle sample to the investigators.

  • Use hemagglutination inhibition and microneutralization procedures to examine sera.

  • Hypotheses testing will be performed for any swine (H1, H3) or avian (H3, H4, H5, H6, H7, H9) influenza hemagglutinin type and later stratified by each swine and avian type.

  • Serologic results will be adjusted for antibodies to human influenza virus.

  • 803 rural Iowans enrolled from 29 counties

  • Enrollment characteristics compared to nonexposed University of Iowa control group (Table 1)

Coinvestigators - Troy McCarthy, Ana W. Capuano, MPS, Charles F. Lynch, MD, PhD, Debbie A. Wellman, Kelly A. Lesher, Sharon F. Setterquist, MT(ASCP), Norma J. Miller, Patricia A P Gillette, MPH, Christopher W. Olsen, DVM, PhD, Alexander I. Klimov, PhD, Michael C. Alavanja, PhD, and Jackie M. Katz, PhD

Collaborators - Kevin Knudson, PhDCEID Staff - Whitney Baker, Mark Lebeck, Ghazi Kayali

Funding – NIH / NIAID- R21 AI059214-01

  • 721 (90 %) participated in the 12-month follow-up.

  • Thus far 64 influenza-like-illness specimens have been received, and 16 influenza A isolates have been recovered: 15 human H3N2 and 1 swine H1N? virus.

  • After only 12 months of follow-up, the exposed have evidence of an increase in antibody titer against both swine influenza viruses that is not explained by antibodies to human H1 viruses (Table 4).