CDC A(H5N1) Bird Flu Response Update
CDC continues to respond to the public health challenge posed by a multistate outbreak of avian influenza A(H5N1) virus, or "H5N1 bird flu," in dairy cows, poultry and other animals in the United States. CDC is working in collaboration with the U.S. Department of Agriculture (USDA), the Food and Drug Administration (FDA), Administration for Strategic Preparedness and Response (ASPR), state public health and animal health officials, and other partners using a One Health approach.
Since April 2024, 20 human cases of avian influenza A(H5) virus infection have been reported in the United States; 21 in total since 2022. Ten of these cases were associated with exposure to H5N1 bird flu-infected poultry and nine were associated with exposure to sick or infected dairy cows 12. This includes six cases in California, two of which were confirmed by CDC on Thursday, October 3, two on Wednesday, October 9, and two on Thursday, October 10. All California cases occurred in dairy workers on affected farms. All of the California cases are from different farms, except for one case reported this week, which was from a farm that had a case reported previously. The two cases from the same affected farm worked on different parts of the farm and are not close contacts of each other. The epidemiology of the situation continues to suggest sporadic instances of animal-to-human spread. All six California cases are reported to have experienced mild symptoms, including eye redness or discharge (conjunctivitis), and none were hospitalized. Additional testing is ongoing in California, and presumptive positives are being routinely forwarded to CDC for confirmatory testing. Going forward, CDC will track and report confirmed cases, by state and source of exposure, in a table on its website. The source of the exposure in one case, which was reported by Missouri on September 6, could not be determined. Serological tests of the contacts of the Missouri case are pending. CDC believes the immediate risk to the general public from H5N1 bird flu remains low, but people with exposure to infected animals are at higher risk of infection.
On the animal health side, USDA is reporting that 299 dairy herds in 14 U.S. states have confirmed cases of H5 bird flu virus infections in dairy cows. The number of affected herds continues to grow nationally, fueled by increases in California. Last week, USDA reported 56 affected dairy herds in California as of October 3. That number increased to 100 by October 11. USDA reports that since April 2024, there have been H5 detections in 36 commercial flocks and 26 backyard flocks, for a total of 18.75 million birds affected.
