Abstract
BACKGROUND: Highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b was first detected in birds in the United States in 2021 and an ongoing outbreak in dairy cattle began in early 2024. At least 70 U.S. cases have been identified in humans with exposure to infected cattle, poultry, and wild birds. No human-to-human transmission has been documented. However, as part of diagnostic preparedness, we evaluated the ability of currently available influenza tests to detect 2024 U.S. H5N1 strains. METHODS: Contrived nasal swab samples were prepared using live or inactivated 2024 H5N1 and used to test twelve rapid antigen tests (lateral flow assays, or LFA), including 10 commercially-available influenza A LFAs and two H5-specific LFAs. Five point-of-care (POC) molecular assays were also tested. An inclusivity testing protocol was used, wherein a predetermined dilution series is used to evaluate each assay, enabling head-to-head comparison of assay performance. RESULTS: All lateral flow assays and POC molecular tests were able to detect bovine 2024 H5N1 (genotype B3.13). Sensitivity for the POC molecular tests (heat-inactivated virus) ranged from 1.55 to 7.75 TCID50/swab. For 11/12 LFAs, including 10 commercial influenza A tests and an RUO H5 assay, sensitivity (live virus) ranged from 78-1550 TCID50/swab. Testing of four LFAs confirmed inclusivity for a genotype D1.1 strain. CONCLUSIONS: Available rapid antigen and point-of-care molecular influenza tests can detect 2024 U.S. H5N1 strains in contrived samples, with a wide range of analytical sensitivity. In the event of human-to-human transmission, clinical performance and optimal sample types would need to be established. SUMMARY: Recent human infections with H5N1 influenza necessitate diagnostic preparedness. Reassuringly, commercially available rapid antigen and point-of-care molecular influenza tests detected the 2024 U.S. bovine H5N1 strain in contrived specimens. Clinical performance should be evaluated if human-to-human transmission is observed.