October 3, 2024 – CDC has confirmed two human cases of H5 bird flu from specimens submitted by California. The cases occurred in people with occupational exposure to infected dairy cows. An investigation led by California is ongoing. The identification of H5 in people with exposure to infected animals is not unexpected and does not change CDC’s risk assessment for the general public, which continues to be low. At this time, there is no known link or contact between the first and second confirmed cases in California, suggesting these are separate instances of animal-to-human spread of the virus. CDC continues to collaborate closely with California and other state public health officials to support state-run efforts to control the spread of H5N1 from infected animals to humans; California’s active monitoring highlights the steps being taken at the state level to lower the risk to farm workers who may be in contact with animals with H5N1.In the coming days, CDC will conduct additional characterization of the viruses, including sequencing, isolating and growing the viruses, if possible.

These are the first human cases of H5 in California, where H5N1 outbreaks among dairy herds were first reported in August 2024. H5N1 bird flu was detected for the first time in cows this year in the United States. The virus is widespread in wild birds and has caused ongoing outbreaks among poultry in the United States since 2022. It has caused rare, sporadic infections in people who work with infected animals, such as dairy cow workers and poultry workers. Including this most recent case, 16 human cases of H5 have been reported in the United States during 2024, bringing the total to 17 cases since 2022. Cases during 2024 have been reported in Texas (1), Michigan (2), Colorado (10), Missouri (1) and California (2). Six of the 16 reported human cases have been linked to exposure to sick or infected dairy cows. Nine cases had exposure to infected poultry. The source of infection for the one case in Missouri has not been determined. Serologic testing of contacts of the case in Missouri is ongoing. CDC has recommendations to protect people against H5N1 bird flu in dairy cattle. These include avoiding contact with wild birds and sick or dead animals and not preparing or eating unpasteurized (raw) milk or raw cheese. If you work with dairy cows or other animals that could be infected with H5N1 bird flu, wear personal protective equipment (PPE) when in contact with (or around) dairy cows, raw milk, other animals, or surfaces and other items that might be contaminated with virus. CDC recently issued updated personal protective equipment guidance (PPE) to prevent H5N1 bird flu infection.

CDC recommends that if you get sick after close contact with infected animals, contact your local health department and a health care provider for testing. Symptoms of H5 include eye redness (conjunctivitis), mild flu-like upper respiratory symptoms, fever, cough, sore throat, difficulty breathing, runny or stuffy nose, and muscle aches.