Investigation of an Outbreak of Variant Influenza A(H3N2) Virus Infection Associated With an Agricultural Fair-Ohio, August 2012

J Infect Dis. 2015 Nov 15;212(10):1592-9. doi: 10.1093/infdis/jiv269. Epub 2015 May 5.


Background: In 2012, one third of cases in a multistate outbreak of variant influenza A(H3N2) virus ([H3N2]v) infection occurred in Ohio. We conducted an investigation of (H3N2)v cases associated with agricultural Fair A in Ohio.

Methods: We surveyed Fair A swine exhibitors and their household members. Confirmed cases had influenza-like illness (ILI) and a positive laboratory test for (H3N2)v, and probable cases had ILI. We calculated attack rates. We determined risk factors for infection, using multivariable log-binomial regression.

Results: We identified 20 confirmed and 94 probable cases associated with Fair A. Among 114 cases, the median age was 10 years, there were no hospitalizations or deaths, and 82% had swine exposure. In the exhibitor household cohort of 359 persons (83 households), we identified 6 confirmed cases (2%) and 40 probable cases (11%). An age of <10 years was a significant risk factor (P < .01) for illness. One instance of likely human-to-human transmission was identified.

Conclusions: In this (H3N2)v outbreak, no evidence of sustained human-to-human (H3N2)v transmission was found. Our risk factor analysis contributed to the development of the recommendation that people at increased risk of influenza-associated complications, including children aged <5 years, avoid swine barns at fairs during the 2012 fair season.

Keywords: influenza; outbreak; variant influenza virus.

MeSH terms

  • Adolescent
  • Adult
  • Age Factors
  • Aged
  • Animals
  • Child
  • Child, Preschool
  • Cohort Studies
  • Crowding*
  • Disease Outbreaks*
  • Disease Transmission, Infectious
  • Female
  • Humans
  • Infant
  • Influenza A Virus, H3N2 Subtype / classification*
  • Influenza A Virus, H3N2 Subtype / genetics
  • Influenza A Virus, H3N2 Subtype / isolation & purification*
  • Influenza, Human / epidemiology*
  • Influenza, Human / virology*
  • Male
  • Middle Aged
  • Occupational Exposure*
  • Ohio / epidemiology
  • Risk Factors
  • Swine
  • Young Adult