Three Human Cases of Bird Flu Detected in California

On Oct. 3, the U.S. Centers for Disease Control and Prevention (CDC) confirmed two human cases of bird flu among workers who were exposed to infected dairy cows. On Saturday, the California Department of Public Health identified a third possible human case of bird flu and is awaiting confirmation from the CDC. The identification of bird flu in people with exposure to infected animals is not unexpected and does not change CDC’s risk assessment for the public, which continues to be low. 

At this time, the two confirmed and one unconfirmed cases in California have no known link, as the people worked on different dairy farms in California’s Central Valley. This suggests the three cases are separate instances of animal-to-human spread of the virus. All three humans have experienced mild symptoms, including eye redness or discharge (conjunctivitis). None of the individuals have been hospitalized. 

Including these most recent cases, 17 human cases of bird flu have been reported in the U.S. during 2024, bringing the total to 18 cases since 2022. Cases during 2024 have been reported in Texas (1), Michigan (2), Colorado (10), Missouri (1), and California (3). Six of the 17 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 yet been determined.

While these are the first human cases of bird flu in California, bird flu outbreaks among dairy herds were first reported in the state in August 2024. Bird flu was detected for the first time in cows this year in the U.S., as CMM previously reported. The virus is widespread in wild birds and has caused ongoing outbreaks among poultry in the United States since 2022.

CDC has recommendations to protect people against bird flu. 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 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 PPE to prevent bird flu infection. 

As CMM previously reported, the World Health Organization said an Argentinian bird flu vaccine developer will share its data with manufacturers in low- and middle-income countries to accelerate a vaccine rollout if a bird flu pandemic occurs.