Influenza A (H3N2) variant virus outbreak at three fairs - Maryland, 2017

Authors: DUWELL, MONIQUE - Centers For Disease Control And Prevention (CDC) - United States; BLYTHE, DAVID - Maryland Department Of Health And Mental Hygiene; RADEBAUGH, MICHAEL - Maryland Department Of Agriculture; KOUGH, ERIN - Maryland Department Of Health And Mental Hygiene; BACHAUS, BRIAN - Maryland Department Of Health And Mental Hygiene; CRUM, DAVID - Maryland Department Of Health And Mental Hygiene; PERKINS JR, KEITH - Maryland Department Of Health And Mental Hygiene; BLANTON, LENEE - Centers For Disease Control And Prevention (CDC) - United States; DAVIS, TODD - Centers For Disease Control And Prevention (CDC) - United States; JANG, YUNHO - Centers For Disease Control And Prevention (CDC) - United States; Baker, Amy; CHANG, JENNIFER - Orise Fellow; ABNEY, DIANNA - Maryland Department Of Health And Mental Hygiene; GUDMUNDSON, LISA - Maryland Department Of Health And Mental Hygiene; BREWSTER, MEENAKSHI - Maryland Department Of Health And Mental Hygiene; POLSKY, LARRY - Maryland Department Of Health And Mental Hygiene; ROSE, DAVID - Maryland Department Of Health And Mental Hygiene; FELDMAN, KATHERINE - Maryland Department Of Health And Mental Hygiene

Submitted to: Morbidity and Mortality Weekly Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2018
Publication Date: 10/26/2018
Citation: Duwell, M., Blythe, D., Radebaugh, M.W., Kough, E.M., Bachaus, B., Crum, D.A., Perkins Jr., K.A., Blanton, L., Davis, T., Jang, Y., Vincent, A.L., Chang, J., Abney, D.E., Gudmundson, L., Brewster, M.G., Polsky, L., Rose, D., Feldman, K.A. 2018. Influenza A (H3N2) variant virus outbreak at three fairs - Maryland, 2017. Morbidity and Mortality Weekly Reports. 67(42):1169-1173. https://doi.org/10.15585/mmwr.mm6742a1.
DOI: https://doi.org/10.15585/mmwr.mm6742a1

Interpretive Summary: Influenza A virus (IAV) is a significant health burden to human and swine populations, and IAV are sporadically shared between the two hosts. When humans are infected with a swine IAV, it is termed "variant" to differentiate it from typical human seasonal strains. In September 2017, the Maryland Department of Agriculture and the Maryland Department of Health conducted a joint investigation of outbreaks of influenza-like illness (ILI) in exhibited swine and in exhibitors and attendees at 3 Maryland county fairs. In total, 80 fair attendees with ILI were identified, of whom 76 underwent influenza testing. Forty (52.6%) people tested presumptive positive for influenza A(H3N2) variant (H3N2v) virus infection. All 40 were subsequently confirmed influenza A(H3N2v) virus positive by additional testing and genetic sequencing analysis performed at the CDC. Samples were collected from pigs at 2 of the 3 fairs and tested positive for H3N2 at the National Veterinary Services Laboratory. Sequence analysis indicated that the H3N2 IAV strains isolated from the pigs and people were nearly identical. This outbreak emphasizes the ongoing public health risk that variant influenza presents in agricultural fair settings. The large proportion of ill children in this outbreak, including 2 hospitalized patients, underscores the vulnerability of children to variant influenza virus and its potential life-threatening complications. Strategies to prevent potential influenza transmission at agricultural fairs might include enhanced surveillance for swine illness, public educational campaigns about influenza virus risk and prevention, and consideration of limiting public access to certain swine exhibits. Lastly, this outbreak emphasizes the collaborative, One Health approach needed to investigate and respond to variant influenza virus outbreaks, including the application of both swine and human infection control measures.

Technical Abstract: On September 17, 2017, the Maryland Department of Agriculture (MDA) received a report of ill swine at agricultural Fair A, which was held September 14-17. MDA's investigation revealed multiple swine with fever and signs of respiratory illness, and they collected respiratory specimens from 5 swine for influenza testing. On September 18, the MDA Animal Health Laboratory reported that all 5 specimens tested positive for influenza A virus. That same day, MDA received reports that children who were swine exhibitors were also ill, prompting notification of the Maryland Department of Health (MDH). A joint investigation with the local health department was launched and was subsequently broadened to Maryland agricultural Fairs B, held September 13-17, and C, held September 15-23, and promoted cancelation of swine exhibits at two subsequent fairs. Forty cases of influenza A(H3N2) variant (A(H3N2)v) virus infections associated with exposure to swine at 1 of these 3 fairs were identified. Of the 40 patients, 75% were at high risk for serious influenza complications: 60% were children aged < 5 years, 15% had a chronic illness, and 2.5% were adults aged =65 years. Most patients (65%) reported direct exposure to swine, defined as touching or handling of swine or swine enclosures, but 35% reported only indirect exposure, such as walking past swine or being pushed in a stroller through a swine barn. Two children required hospitalization, one of whom was critically ill; all patients recovered. This outbreak highlights the risk of contracting variant influenza virus in agricultural fair settings following direct or indirect swine exposure, particularly among young children. The Centers for Disease Control and Prevention (CDC) recommends that children aged <5 years and others at high risk for serious influenza complications avoid pigs and swine barns, and publicizing this recommendation to fairgoers might help to prevent future variant influenza outbreaks among vulnerable groups.