Extreme heat may have contributed to the illnesses of five workers who fell sick last week while culling a large flock of chickens infected with the H5N1 virus in Colorado, health officials reported on Tuesday.
Dr. Nirav Shah, the principal deputy director of the US Centers for Disease Control and Prevention (CDC), noted that Colorado was experiencing temperatures above 104 degrees at the time of transmission, with even higher temperatures inside the barns. To cool down the sweltering barns, large industrial fans were used, which not only circulated air but also dust and feathers—potential carriers of the H5N1 virus.
“These large fans were moving so much air that workers struggled to maintain a proper fit with their masks and eye protection,” Dr. Shah explained.
The CDC, working with the Colorado Department of Public Health and Environment, has confirmed four of the cases, with a fifth still awaiting confirmation from the CDC after testing positive at a state lab.
This outbreak has significantly increased the number of known H5N1 infections among farm workers in the U.S. The current cases in Colorado, Texas, Michigan, and another Colorado case mark the largest cluster of infections linked to a single farm. Previous to this, only one poultry worker in Colorado had tested positive for H5N1 in 2022.
Genetic analysis of the virus from these recent cases showed no concerning mutations that might suggest easier human-to-human transmission. The virus closely resembles the strain affecting cattle.
In response to the outbreak, the CDC has deployed a 10-person team to assist with the investigation and contact tracing. Of the 60 individuals who exhibited symptoms similar to bird flu, all but five have tested negative. The culling operation, which involves 160 workers killing 1.8 million chickens, is expected to last another 10 to 14 days.
While the exact source of the bird infection remains unclear, the viruses isolated from the chickens are closely related to those infecting dairy cattle, according to Dr. Eric Deeble of the USDA.
Although the risk to the general public from H5N1 remains low, farm workers are at higher risk due to their exposure. The CDC advises those handling sick or dead birds and cattle to wear full personal protective equipment (PPE), including coveralls, masks, goggles, gloves, and boots. However, the intense heat has made it challenging for workers to use PPE effectively.
Elizabeth Strater of the United Farm Workers labor union has criticized the CDC's guidelines, highlighting the difficulty of adhering to PPE recommendations in extreme heat conditions. She urged the CDC to reconsider its recommendations and explore vaccination options for farm workers, as is being done in Finland.
The CDC is currently refining its PPE recommendations to better accommodate the heat. Additionally, the U.S. Department of Health and Human Services has ordered 4.8 million doses of an H5N1 vaccine, with production expected to be completed by the end of the month. HHS has also invested in the development of an mRNA-based H5N1 vaccine with Moderna, with safety results anticipated by year-end.
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