Agricultural fairs provide an opportunity for bidirectional transmission of influenza A viruses. We sought to determine influenza A virus activity among swine at fairs in the United States. As part of an ongoing active influenza A virus surveillance project, nasal swab samples were collected from exhibition swine at 40 selected Ohio agricultural fairs during 2012. Influenza A(H3N2) virus was isolated from swine at 10 of the fairs. According to a concurrent public health investigation, 7 of the 10 fairs were epidemiologically linked to confirmed human infections with influenza A(H3N2) variant virus. Comparison of genome sequences of the subtype H3N2 isolates recovered from humans and swine from each fair revealed nucleotide identities of >99.7%, confirming zoonotic transmission between swine and humans. All influenza A(H3N2) viruses isolated in this study, regardless of host species or fair, were >99.5% identical, indicating that 1 virus strain was widely circulating among exhibition swine in Ohio during 2012. In the United States during 2012, approximately 300 cases of human infection with influenza A(H3N2) variant (H3N2v) virus were reported; they resulted in 16 hospitalizations and 1 death. The variant designation (swine-origin influenza A virus infecting humans) of these cases must be acknowledged because interspecies transmission of influenza A virus plays a substantial role in the evolution of influenza A viruses that infect swine and humans. Genomic reassortment resulting in novel influenza A viruses can occur in swine because they are susceptible hosts for avian and human strains as well as strains endemic among swine. Thus, swine play a critical role in the ecology and emergence of influenza A viruses that affect human health, as illustrated by the emergence of the 2009 pandemic influenza virus (influenza A[H1N1]pdm09 virus), a reassortant virus with origins that have been traced to influenza A viruses circulating among swine in North America and Eurasia. Bidirectional transmission of influenza A viruses between swine and humans is facilitated by unique swine–human interfaces such as agricultural fairs, where swine from multiple sources commingle with human exhibitors and visitors. In 2007, novel influenza A viruses, including those of nonhuman origin, became part of the National Notifiable Diseases Surveillance System, and before 2012, outbreaks of variant influenza A virus were reported only occasionally in the medical literature; these cases were frequently linked to human exposure to swine at agricultural fairs. Epidemiologic investigations by public health officials into human cases of influenza virus subtype H3N2v infection that occurred during 2012 concluded that swine exposure at agricultural fairs was the primary source of the viruses.
http://wwwnc.cdc.gov/eid/ Emerging Infectious Diseases
http://wwwnc.cdc.gov/eid/article/20/9/13-1082_article Original web page at Emerging Infectious Diseases