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, 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.

Swine Influenza A Viruses and the Tangled Relationship with Humans

“…The H3N2v cases were from two lineages of H3 that circulate in the United States. Before 2016, H3N2v infections were caused by viruses containing HA genes from the 1990.4 C-IV H3 lineage (Jhung et al 2013;Greenbaum et al 2015). Although originally derived from human seasonal H3 viruses circulating in the 1990s, these viruses are antigenically distinct from contemporary seasonal H3N2 in humans, prompting the development of candidate vaccine viruses (CVVs) targeting the 1990.4 C-IV viruses (https://www.who.int/ influenza/resources/documents/2011_09_h5_ h9_vaccinevirusupdate.pdf?ua=1).…”

“…This diversity and the human-swine interface are incredibly important in the context of variant IAV infections in humans. Dramatic increases in the detection of variant IAV infections began with H3N2 viruses in the United States in 2012 (Epperson et al 2013), and these viruses are regularly detected in the United States (Jhung et al 2013;Choi et al 2015;Greenbaum et al 2015;Duwell et al 2018;Pulit-Penaloza et al 2018a) and to a lesser degree in other countries (Resende et al 2017;Xie et al 2018;Lu et al 2019). The risk of variant infection is likely dependent on animal production systems, animal-human interfaces (e.g., live animal markets, exhibition practices), the ecology of the virus, and other less tangible factors (Karesh et al 2012).…”

Amino Acids in Hemagglutinin Antigenic Site B Determine Antigenic and Receptor Binding Differences between A(H3N2)v and Ancestral Seasonal H3N2 Influenza Viruses

“…(2)(3)(4), with more than 300 laboratoryconfirmed cases in 2011 alone (5,6). Most of the A(H3N2)v cases have been children who had contact with swine at agricultural fairs (5,7,8). Fortunately the symptoms of A(H3N2)v infection were generally mild, although some patients had to be hospitalized, and one case was fatal (9).…”

Text-Based Illness Monitoring for Detection of Novel Influenza A Virus Infections During an Influenza A (H3N2)v Virus Outbreak in Michigan, 2016: Surveillance and Survey (Preprint)

“…In the United States, human infection with a novel influenza A virus is nationally notifiable [1]. In the United States, swine are the primary source of reported novel influenza A virus infections in humans, and the vast majority of persons are infected after swine exposure at an agricultural fair [2][3][4][5][6][7][8][9]. Some influenza A viruses are endemic pathogens in swine populations [10][11][12][13] and swine can be infected without displaying clinical signs of illness [14].…”