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Volume 31, Number 12—December 2025

Dispatch

Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus Infection in Poultry Farm Workers, Washington, USA, 2024

Yasuko Hatta1, Juan A. De La Cruz1, Theresa Murray, Brian Hiatt, Yunho Jang, Julia C. Frederick, Kristine A. Lacek, Juliana C. DaSilva, Dan Cui, Paul Carney, Jimma Liddell, Kay W. Radford, Natasha Burnett, Sabrina Schatzman, Pauline Trinh, Anna Unutzer, Elizabeth A. Pusch, Monique Johnson, Ha T. Nguyen, Benjamin L. Rambo-Martin, Larisa Gubareva, James Stevens, C. Todd Davis, Marie K. Kirby, Allison Black, and Han DiComments to Author 
Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA (Y. Hatta, J.A. De La Cruz, Y. Jang, J.C. Frederick, K.A. Lacek, J.C. DaSilva, D. Cui, P. Carney, J. Liddell, K.W. Radford, N. Burnett, S. Schatzman, E.A. Pusch, M. Johnson, H.T. Nguyen, B.L. Rambo-Martin, L. Gubareva, J. Stevens, C.T. Davis, M.K. Kirby, H. Di); Washington State Department of Health, Shoreline, Washington, USA (T. Murray, B. Hiatt, P. Trinh, A. Unutzer, A. Black)

Main Article

Table

Hemagglutination inhibition testing of highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b genotype D1.1 viruses isolated from poultry farm workers, Washington, USA, 2024*

Antigens Subtype Clade Hemagglutination inhibition titer†
CDC-RG RG71A RG71A RG78A RG78A NIID-002 TX/37
Reference antigens
CDC-RG, A/Vietnam/1203/2004 H5N1 1 2,560 <10 <10 <10 <10 <10 <10
IDCDC-RG71A, A/Astrakhan/3212/2020 H5N8 2.3.4.4b 10 160 160 80 80 40 <10
IDCDC-RG78A, A/American Wigeon/South Carolina/22-000345-001/2021 H5N1 2.3.4.4b 10 160 160 160 320 80 80
NIID-002, A/Ezo red fox/Hokkaido/1/2022 H5N1 2.3.4.4b 10 160 320 160 160 80 80
A/Texas/37/2024
 H5N1
 2.3.4.4b
 10
 80
 80
 160
 160
 80
 80
Test antigens
A/Washington/239/2024, conjunctival‡ H5N1 2.3.4.4b 10 80 160 160 160 80 80
A/Washington/240/2024, conjunctival§ H5N1 2.3.4.4b 10 80 80 160 160 40 40
A/Washington/240/2024, nasopharyngeal§ H5N1 2.3.4.4b 10 80 80 320 320 80 80
A/Washington/254/2024, conjunctival§ H5N1 2.3.4.4b 10 80 40 160 160 80 80
A/Washington/255/2024, conjunctival§ H5N1 2.3.4.4b 10 40 40 160 160 80 40

*Bold indicates homologous titers. TX/37, A/Texas/37/2024. †Two different lots of ferret antiserum against RG71A or RG78A were used in this test. ‡Isolated on MDCK cells. §Isolated on 10–11-day old embryonated chicken eggs.

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1These authors contributed equally to this article.

Page created: November 20, 2025
Page updated: December 23, 2025
Page reviewed: December 23, 2025
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