Outbreak of variant influenza A(H3N2) virus in the United States

Michael A. Jhung, Scott Epperson, Matthew Biggerstaff, Donna Allen, Amanda Balish, Nathelia Barnes, Amanda Beaudoin, LaShondra Berman, Sally Bidol, Lenee Blanton, David Blythe, Lynnette Brammer, Tiffany D'mello, Richard Danila, William Davis, Sietske De Fijter, Mary Diorio, Lizette O. Durand, Shannon Emery, Brian FowlerRebecca Garten, Yoran Grant, Adena Greenbaum, Larisa Gubareva, Fiona Havers, Thomas Haupt, Jennifer House, Sherif Ibrahim, Victoria Jiang, Seema Jain, Daniel Jernigan, James Kazmierczak, Alexander Klimov, Stephen Lindstrom, Allison Longenberger, Paul Lucas, Ruth Lynfield, Meredith Mcmorrow, Maria Moll, Craig Morin, Stephen Ostroff, Shannon L. Page, Sarah Y. Park, Susan Peters, Celia Quinn, Carrie Reed, Shawn Richards, Joni Scheftel, Owen Simwale, Bo Shu, Kenneth Soyemi, Jill Stauffer, Craig Steffens, Su Su, Lauren Torso, Timothy M. Uyeki, Sara Vetter, Julie Villanueva, Karen K. Wong, Michael Shaw, Joseph S. Bresee, Nancy Cox, Lyn Finelli

Research output: Contribution to journalArticlepeer-review

137 Scopus citations


Background. Variant influenza virus infections are rare but may have pandemic potential if person-to-person transmission is efficient. We describe the epidemiology of a multistate outbreak of an influenza A(H3N2) variant virus (H3N2v) first identified in 2011.Methods. We identified laboratory-confirmed cases of H3N2v and used a standard case report form to characterize illness and exposures. We considered illness to result from person-to-person H3N2v transmission if swine contact was not identified within 4 days prior to illness onset.Results. From 9 July to 7 September 2012, we identified 306 cases of H3N2v in 10 states. The median age of all patients was 7 years. Commonly reported signs and symptoms included fever (98%), cough (85%), and fatigue (83%). Sixteen patients (5.2%) were hospitalized, and 1 fatal case was identified. The majority of those infected reported agricultural fair attendance (93%) and/or contact with swine (95%) prior to illness. We identified 15 cases of possible person-to-person transmission of H3N2v. Viruses recovered from patients were 93%-100% identical and similar to viruses recovered from previous cases of H3N2v. All H3N2v viruses examined were susceptible to oseltamivir and zanamivir and resistant to adamantane antiviral medications.Conclusions. In a large outbreak of variant influenza, the majority of infected persons reported exposures, suggesting that swine contact at an agricultural fair was a risk for H3N2v infection. We identified limited person-to-person H3N2v virus transmission, but found no evidence of efficient or sustained person-to-person transmission. Fair managers and attendees should be aware of the risk of swine-to-human transmission of influenza viruses in these settings.

Original languageEnglish (US)
Pages (from-to)1703-1712
Number of pages10
JournalClinical Infectious Diseases
Issue number12
StatePublished - Dec 2013


  • influenza
  • outbreak
  • pandemic
  • variant influenza


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