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United States Department of Agriculture

Agricultural Research Service

Research Project: INTERVENTION STRATEGIES TO CONTROL VIRAL DISEASES OF SWINE Title: Human infections with influenza A(H3N2) variant virus in the United States, 2011-2012

Authors
item Epperson, Scott -
item Jhung, Michael -
item Richards, Shawn -
item Quinlisk, Patricia -
item Ball, Lauren -
item Moll, Maria -
item Boulton, Rachelle -
item Haddy, Loretta -
item Biggerstaff, Matthew -
item Brammer, Lynnette -
item VINCENT, AMY

Submitted to: Clinical Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 24, 2013
Publication Date: July 1, 2013
Citation: Epperson, S., Jhung, M., Richards, S., Quinlisk, P., Ball, L., Moll, M., Boulton, R., Haddy, L., Biggerstaff, M., Brammer, L., Trock, S., Burns, E., Gomez, T., Wong, K.K., Katz, J., Lindstrom, S., Klimov, A., Bresee, J.S., Jernigan, D.B., Cox, N., Finelli, L., Influenza A(H3N2)v Virus Investigation Team (Vincent, A.L.). 2013. Human infections with influenza A(H3N2) variant virus in the United States, 2011-2012. Clinical Infectious Diseases. 57(S1):S4-S11.

Interpretive Summary: During August 2011–April 2012, 13 human infections with influenza A(H3N2) variant (H3N2v) virus related to H3N2 that circulate in swine were identified in the United States; 8 occurred in the prior 2 years. This virus differs from previous variant influenza viruses in that it contains the matrix (M) gene from the influenza A(H1N1)pdm09 pandemic influenza virus. A case was defined as a person with laboratory-confirmed H3N2v virus infection. Cases and contacts were interviewed to determine exposure to swine and other animals and to assess potential person-to-person transmission. Median age of cases was 4 years, and 12 of 13 (92%) were children. Pig exposure was identified in 7 (54%) cases. Six of 7 cases with swine exposure (86%) touched pigs, and 1 (14%) was close to pigs without known direct contact. Six cases had no swine exposure, including 2 clusters of suspected spread among people without swine contact. All cases had fever; 12 (92%) had respiratory symptoms, and 3 (23%) were hospitalized for influenza. All 13 cases recovered. Variant influenza viruses rarely spread from person-to-person; however, the potential for this H3N2v virus to transmit to and between humans if of concern. With minimal preexisting immunity in children and the limited cross-protective effect from seasonal influenza vaccine, the children may be particularly susceptible to infection with this novel influenza virus.

Technical Abstract: BACKGROUND. During August 2011-April 2012, 13 human infections with influenza A(H3N2) variant (H3N2v) virus were identified in the United States; 8 occurred in the prior 2 years. This virus differs from previous variant influenza viruses in that it contains the matrix (M) gene from the Influenza A(H1N1)pdm09 pandemic influenza virus. METHODS. A case was defined as a person with laboratory-confirmed H3N2v virus infection. Cases and contacts were interviewed to determine exposure to swine and other animals and to assess potential person-to-person transmission. RESULTS. Median age of cases was 4 years, and 12 of 13 (92%) were children. Pig exposure was identified in 7 (54%) cases. Six of 7 cases with swine exposure (86%) touched pigs, and 1 (14%) was close to pigs without known direct contact. Six cases had no swine exposure, including 2 clusters of suspected person-to-person transmission. All cases had fever; 12 (92%) had respiratory symptoms, and 3 (23%) were hospitalized for influenza. All 13 cases recovered. CONCLUSIONS. H3N2v virus infections were identified at a high rate from August 2011 to April 2012, and cases without swine exposure were identified in influenza-like illness outbreaks, indicating that limited person-to-person transmission likely occurred. Variant influenza viruses rarely result in sustained person-to-person transmission; however, the potential for this H3N2v virus to transmit efficiently is of concern. With minimal preexisting immunity in children and the limited cross-protective effect from seasonal influenza vaccine, the majority of children are susceptible to infection with this novel influenza virus.

Last Modified: 9/29/2014
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