A fourth individual in the United States has been confirmed positive for H5 bird flu, linked to an ongoing outbreak among dairy cattle nationwide.
The Colorado Department of Public Health and Environment announced its first human case of H5 avian influenza related to the multistate outbreak in dairy cattle. This marks the fourth case in the nation, with two cases reported in Michigan and one in Texas.
Data from the Colorado state health department shows that over a quarter of the state’s dairy herds have reported bird flu cases. Federal data indicates that seven states have confirmed cases in the last 30 days, with 40% of those cases in Colorado, the highest of any state.
The infected individual in Colorado experienced mild symptoms, specifically conjunctivitis (pink eye). The person worked at a dairy farm in northeast Colorado and had direct exposure to avian flu-infected cattle. After testing positive, the person received antiviral treatment with oseltamivir and has since recovered.
Dr. Rachel Herlihy, state epidemiologist at the CDPHE, emphasized that the risk to the general public remains low. The avian flu virus is currently spreading among animals but is not adapted for human-to-human transmission. Those with regular exposure to infected animals are at higher risk and should take precautions when in contact with sick animals. The last human case of H5N1 in Colorado was in 2022 in an individual exposed to infected poultry.
In the current outbreak, the first two human cases reported eye-related symptoms, while the third case experienced respiratory symptoms such as cough, congestion, sore throat, and watery eyes. None of these cases involved contact with each other but were linked to working with cattle, indicating cow-to-human transmission.
The US Centers for Disease Control and Prevention (CDC) is closely monitoring the situation using flu surveillance systems. The recent human case in Colorado has not changed the CDC’s assessment of the H5N1 bird flu risk to the general public, which remains low. However, it highlights the need for recommended precautions for those exposed to infected animals.
The CDC advises dairy workers to wear personal protective equipment to mitigate their risk. The US Department of Agriculture is providing financial support to farms with infected animals to ensure worker protection. Ongoing research aims to understand how the virus transmits between cows and from cows to humans.
CDC officials have assured that the United States has sufficient H5 bird flu tests to manage the outbreak. Dr. Nirav Shah, principal deputy director of the CDC, confirmed that there are approximately 750,000 H5-specific tests available, with an additional 1.2 million tests expected in the next two to three months. Influenza A tests are also widely available, and specimens testing positive for influenza A are sent to public health labs for subtyping to identify specific strains like H5N1.
