US and Colorado Investigate Further H5N1 Bird Flu Cases at Poultry Farm

Federal and state investigators in Colorado are probing an outbreak of H5N1 bird flu at a poultry farm, which has led to four confirmed human cases and one suspected case.

These infections mark the first reported instances of H5N1 in poultry workers in the United States since 2022. They follow a separate outbreak of H5N1 in U.S. dairy cattle that has infected four additional farm workers since March.

The affected poultry workers were involved in culling chickens at a commercial egg facility in northeast Colorado experiencing a bird flu outbreak, although the specific facility has not been named by the state.

The H5N1 bird flu strain has been spreading globally among wild birds, infecting poultry and various mammal species.

The U.S. Centers for Disease Control and Prevention (CDC), in a statement on July 14, deployed a nine-member field team comprising epidemiologists, veterinarians, clinicians, and an industrial hygienist to assist Colorado in assessing the outbreak and human cases.

CDC emphasized that the risk to the general public remains low but acknowledged this assessment could change. Genetic sequencing of the virus is currently underway to detect mutations indicating potential adaptation to humans.

Symptoms reported by infected workers included mild illness such as conjunctivitis, eye tearing, fever, chills, coughing, sore throat, and runny nose, typical of flu symptoms.

CDC warned that additional cases might be identified as monitoring and testing continue.

Experts noted that while the poultry worker cases are concerning, transmission from poultry to humans is generally less alarming than transmission from dairy cows, which involves a virus that has adapted to mammals over a longer period.

Andrew Pekosz, an influenza expert at Johns Hopkins University, stressed the importance of genetic analysis to compare the virus from infected workers with strains affecting dairy cows.

Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota, highlighted the occupational risks during depopulation operations, emphasizing the need for stringent protective measures including eye protection to prevent conjunctivitis and other infections.