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

Abstract

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, themedian age was 10 years, therewere 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.