An H5N1 outbreak that recently affected five poultry workers and led to the culling of 1.8 million chickens in northeast Colorado may have been exacerbated by extreme heat and the methods used for slaughter, according to federal health authorities.
The U.S. Centers for Disease Control and Prevention (CDC) reported that the human infections occurred while poultry workers were culling infected birds in 104-degree heat. The oppressive conditions made it nearly impossible for workers to wear protective clothing and equipment comfortably, leading to the use of large fans to cool down. These fans, however, likely facilitated the spread of the virus through feathers, dust, and other poultry debris.
Additionally, the method employed to euthanize the infected chickens—carbon dioxide gassing—required workers to move from bird to bird, increasing their interaction with potentially infected animals. This method, considered the “gas of choice” in North America due to its availability and cost-effectiveness, involves placing chickens in a sealed unit where they are exposed to CO2. The gas first renders the birds unconscious before suffocating them, a process that takes less than a minute and a half per group of birds.
Federal officials highlighted that these conditions, coupled with the excessive heat, created a scenario where standard protective measures were difficult to maintain, potentially exposing workers to the virus. The outbreak, which saw four confirmed human cases and one presumptive case awaiting final results, underscores the need for better prevention strategies, including more practical protective equipment and engineering adaptations to reduce exposure risks.
The farm, which was infected earlier this month, had to follow standard industry practice by culling all potentially infected birds and cleaning the premises thoroughly. The outbreak’s scale, given the size of the operation, meant that the culling process took weeks and required workers to handle both live and dead birds, further increasing the risk of virus transmission.
Health officials have noted that the DNA sequencing of the virus obtained from one of the infected poultry workers is closely related to the virus found in the chickens from the farm, as well as to the virus in a dairy worker infected in Texas in April and in infected dairy herds near the Colorado poultry farm. This raises the possibility that the virus could have been transmitted from a nearby dairy herd to the poultry farm, necessitating a full investigation into potential pathways of transmission, which may include worker movements, shared equipment, or environmental factors like groundwater or habitat transmission.
Birds and rodents are known mechanical transmitters, and wild birds frequently visit both dairy and poultry farms. This interaction could further complicate efforts to control the virus’s spread. While poultry farmers have significantly improved their biosecurity measures in recent years, experts note that the dairy industry lags behind in creating effective physical barriers to prevent such outbreaks.
The situation is further complicated by the upcoming fall migration, which could introduce new challenges as the virus potentially spreads to more species and environments. This evolving scenario highlights the unpredictability of the virus’s movement and the ongoing need for vigilant monitoring and adaptive response strategies.
