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United States Department of Agriculture

Agricultural Research Service

Research Project: INTERVENTION STRATEGIES TO CONTROL VIRAL DISEASES OF SWINE

Location: Virus and Prion Research

Title: Human infections with influenza A(H3N2) variant virus in the United States, 2011-2012)

Author
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: 4/24/2013
Publication Date: 7/1/2013
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: 8/24/2016
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