sharon sanders
Editor-in-Chief & President
h/t @greg_folkers
Clinical Microbiology
10 December 2025
One confirmed and one potential human case of influenza A(H5N1) detected through an expanded subtyping protocol
Authors: Grant P. Higerd-Rusli https://orcid.org/0000-0001-8288-576X, Abraar Karan, Seth A. Hoffman https://orcid.org/0000-0002-7881-3605, Ingrid E. A. Morante, ChunHong Huang, Malaya K. Sahoo, Matthew M. Hernandez, Benjamin A. Pinsky https://orcid.org/0000-0001-8751-4810 bpinsky@stanford.eduAuthors Info & Affiliations
https://doi.org/10.1128/asmcr.00165-25
ABSTRACT
Current U.S. surveillance for highly pathogenic avian influenza A(H5N1) in humans prioritizes individuals with known animal exposures, potentially missing community-acquired infections. To address this gap, we implemented universal H5 subtyping of all influenza A-positive respiratory samples collected within our hospital system, regardless of patient exposure history. Between August 2024 and April 2025, we subtyped 4,488 influenza A-positive samples and identified two cases positive for H5 RNA in Alameda County, California, USA.
The first case was a 14-month-old girl with mild respiratory symptoms and no H5N1 exposure risks; sequencing of the sample revealed an H5 gene closely related to clade 2.3.4.4b, genotype B3.13 viruses circulating in U.S. dairies.
The second case was a 79-year-old male, also with no known exposures, whose sample reproducibly tested positive with a high cycle threshold value but could not be confirmed by public health laboratories.
Both patients had evidence of co-infection with other common respiratory viruses. These findings, while requiring cautious interpretation due to low virus levels and the presence of potential confounding factors, highlight limitations in exposure-based testing and demonstrate the potential for cryptic H5N1 circulation. This report underscores that broader, geographically targeted surveillance may be a critical tool for early detection of potential community transmission of pandemic-capable pathogens.
https://journals.asm.org/doi/10.1128/asmcr.00165-25
Clinical Microbiology
10 December 2025
One confirmed and one potential human case of influenza A(H5N1) detected through an expanded subtyping protocol
Authors: Grant P. Higerd-Rusli https://orcid.org/0000-0001-8288-576X, Abraar Karan, Seth A. Hoffman https://orcid.org/0000-0002-7881-3605, Ingrid E. A. Morante, ChunHong Huang, Malaya K. Sahoo, Matthew M. Hernandez, Benjamin A. Pinsky https://orcid.org/0000-0001-8751-4810 bpinsky@stanford.eduAuthors Info & Affiliations
https://doi.org/10.1128/asmcr.00165-25
ABSTRACT
Current U.S. surveillance for highly pathogenic avian influenza A(H5N1) in humans prioritizes individuals with known animal exposures, potentially missing community-acquired infections. To address this gap, we implemented universal H5 subtyping of all influenza A-positive respiratory samples collected within our hospital system, regardless of patient exposure history. Between August 2024 and April 2025, we subtyped 4,488 influenza A-positive samples and identified two cases positive for H5 RNA in Alameda County, California, USA.
The first case was a 14-month-old girl with mild respiratory symptoms and no H5N1 exposure risks; sequencing of the sample revealed an H5 gene closely related to clade 2.3.4.4b, genotype B3.13 viruses circulating in U.S. dairies.
The second case was a 79-year-old male, also with no known exposures, whose sample reproducibly tested positive with a high cycle threshold value but could not be confirmed by public health laboratories.
Both patients had evidence of co-infection with other common respiratory viruses. These findings, while requiring cautious interpretation due to low virus levels and the presence of potential confounding factors, highlight limitations in exposure-based testing and demonstrate the potential for cryptic H5N1 circulation. This report underscores that broader, geographically targeted surveillance may be a critical tool for early detection of potential community transmission of pandemic-capable pathogens.
https://journals.asm.org/doi/10.1128/asmcr.00165-25