There’s been no person-to-person spread, and the human health risk remains low, but some measures of the bird flu do keep creeping up, according to recent reports by the federal Centers for Disease Control and Prevention.
For example, the CDC confirmed a third human case of H5 bird flu in California, following two cases confirmed last week.
The CDC said the latest patient reported occupational exposure to infected dairy cows.
To date, all three California cases have involved dairy workers from three different affected farms who have no known contact with each other, suggesting animal-to-human spread.
Also consistent with the two previous California cases, the new patient experienced mild symptoms, including eye redness or discharge (conjunctivitis). None of the three cases in California have involved hospitalization. The identification of H5N1 bird flu in people with exposure to infected animals is not unexpected and does not change the CDC’s risk assessment for the general public, which continues to be low.
With this most recent case, 18 human cases of H5 bird flu have been reported in the United States since 2022, including 17 cases during 2024. The CDC is awaiting two additional presumptive positive specimens from California for confirmatory testing.
CDC lab update on first two California cases
Sequences from the first two cases in California confirmed these are clade 2.3.4.4b A(H5N1) viruses closely related to viruses detected in dairy cattle. The whole genome was sequenced from one of the two cases (A/California/135/2024) and was confirmed to be a B3.13 genotype virus.
There were no genetic changes observed that are known to be associated with an increased ability to infect or spread between people or known to reduce susceptibility to antiviral medications. These sequences have been publicly posted in GISAID and have been submitted to GenBank
Sequencing from the third confirmed case is underway.
The CDC continues to underscore the importance of recommended precautions for people exposed to infected or potentially infected animals. People with close or prolonged, unprotected exposures to infected birds or other animals, including livestock, or to environments contaminated by infected birds or other animals are at greater risk of infection.
After the human cases, the most troubling reports involve 295 dairy herds in 14 states infected with the H5N1 bird flu. Bird flu has also hit commercial poultry hard, causing the loss of more than 100 million birds.
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