SACRAMENTO – The Centers for Disease Control and Prevention (CDC) has verified two instances of human infection with the H5 strain of avian influenza, both originating from samples provided by the state of California. According to the CDC, these infections occurred in individuals who had direct occupational contact with infected dairy cattle.

State health authorities in California are currently conducting an investigation to understand the full scope of the outbreak. The CDC has stated that while the identification of H5 in people exposed to infected animals is not unexpected,the agency’s risk assessment for the general public remains low.

As of now, there is no identified connection between the two confirmed cases in california, suggesting that these are self-reliant instances of the virus jumping from animals to humans. The CDC is actively collaborating with California and other state public health agencies to support efforts aimed at controlling the spread of H5N1 from infected animals to humans. The CDC plans to further analyze the viruses,including sequencing and attempting to isolate and grow them for research purposes.

These are the first reported human cases of H5 in California,where H5N1 outbreaks among dairy herds were initially reported in August 2024. The H5N1 bird flu virus was first detected in cows in the United States earlier in 2024. The virus is widespread among wild bird populations and has caused ongoing outbreaks among poultry in the United States since 2022. These outbreaks have led to rare, sporadic infections in people who work closely with infected animals, such as dairy and poultry workers.

Including the most recent cases, there have been 17 human cases of H5 reported in the United States since 2022. During 2024, cases 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, while nine cases involved exposure to infected poultry. The source of infection for the case in missouri remains undetermined,and serologic testing of contacts is ongoing.

The CDC provides recommendations for protecting against H5N1 bird flu in dairy cattle, including avoiding contact with wild birds and sick or dead animals, and avoiding the consumption of unpasteurized milk or cheese. For those working with dairy cows or other animals that could be infected, the CDC recommends wearing personal protective equipment (PPE) when in contact with perhaps contaminated animals, raw milk, or surfaces. The CDC has recently updated its PPE guidance to prevent H5N1 bird flu infection.

The CDC advises that individuals who become ill after close contact with infected animals should contact their local health department and seek testing from a healthcare provider. Symptoms of H5 infection can include eye redness (conjunctivitis), mild flu-like upper respiratory symptoms, fever, cough, sore throat, difficulty breathing, runny or stuffy nose, and muscle aches.

The CDC has stated that while the identification of H5 in people exposed to infected animals is not unexpected, the agency’s risk assessment for the general public remains low.