Bird flu has infected six farmworkers in Colorado this month, the highest number in any state, as health officials emphasized the need for preparedness to control the H5N1 virus that is spreading through dairy herds and poultry flocks nationwide. Five of the workers were culling poultry at a commercial egg-laying farm facing an outbreak affecting nearly 2 million chickens, according to Colorado officials.
During a news briefing on Tuesday, federal officials noted that extreme temperatures above 104 degrees made it challenging for workers to wear the required protective gear, including full-body suits, goggles, and N95 masks.
“The barns where the culling operations take place were undoubtedly even hotter,” said Nirav Shah, principal deputy director of the Centers for Disease Control and Prevention (CDC). Industrial fans were used to cool the barns, but they also spread virus-carrying feathers, he added. The culling process involved extensive interaction with infected birds, requiring workers to place chickens in carts that kill them with carbon dioxide gas.
“The workers were struggling to maintain a good seal or fit with their masks and eye protection,” Shah stated. “These factors may explain why the outbreak occurred where and when it did.”
The culling at the farm in Weld County involves 160 workers and will continue for another 10 to 14 days to prevent further spread among the flock, said Eric Deeble, a senior official at the U.S. Department of Agriculture overseeing the bird flu response. About 55 poultry workers with symptoms have been tested, with all negative except for the five workers who tested positive for bird flu. Four cases were confirmed by the CDC, and one presumed positive case is pending confirmation.
An additional 16 symptomatic poultry workers were tested on Monday and are awaiting results, according to Colorado health officials.
Despite the situation, the risk to the general public remains low, officials assured.
Human infection is rare and all U.S. cases have been linked to direct contact with infected cows or poultry, not person-to-person transmission, according to officials.
H5N1 bird flu is widespread among wild birds globally and caused outbreaks in U.S. dairy cows for the first time this spring. Nearly 160 dairy herds have been infected in 13 states, the U.S. Department of Agriculture reported. This highly pathogenic avian influenza strain is deadly to domestic poultry, capable of wiping out entire flocks within days, but causes less severe illness in cows.
Colorado has been significantly affected, with outbreaks in at least 37 dairy herds, including several in Weld County where the poultry workers were infected. Genetic sampling from the chickens shows the same virus type found in nearby infected dairy herds, said USDA’s Deeble.
Earlier in July, a Colorado dairy worker contracted bird flu after being exposed to infected cattle. Officials are investigating links between that dairy worker and the five poultry workers.
Nationwide, a total of nine people, including three other dairy workers—two in Michigan and one in Texas—have been infected with H5N1 this year.
Direct exposure to infected birds increases the risk of contracting the disease, as birds shed flu viruses in saliva, mucus, and feces. Dairy workers can contract the virus through contaminated milk or equipment.
The genetic sequence of the virus from one infected poultry worker may provide more information on how the virus is spreading, officials said. Part of the virus is the same as that found in the Texas worker and one Michigan worker, Shah noted. One theory is that infected dairy cows from Texas were transported to Michigan and Colorado.
“What may be occurring in some cases is spread within very tight regional or local areas,” Shah said. “This could also explain why the virus seen is largely the same, despite appearing in different locations from Michigan to Colorado.”
The CDC is not recommending vaccines for livestock workers against bird flu since all workers who contracted the disease reported mild symptoms. The infected poultry workers experienced eye inflammation and typical flu symptoms, including fever, chills, coughing, sore throat, and runny nose. None required hospitalization.
The CDC has not detected any unusual flu trends in laboratory data or emergency department visits at national, state, or local levels, Shah added.
Preliminary analysis of the virus’ genetic sequence from the poultry worker in Colorado shows no changes that would increase illness severity, facilitate person-to-person transmission, or reduce the effectiveness of Tamiflu treatment, Shah said.
Federal health and agriculture officials have repeatedly stressed the importance of protective measures when working with infected animals. Supplies have been made available to dairy farm owners but their use has not been mandated.
Federal officials on Tuesday praised Colorado’s response to the outbreak. In May, as dairy herds in the state became infected, Colorado requested goggles, gloves, and N95 masks from the federal stockpile. Over the weekend, after tests confirmed infections among the poultry workers, the state asked for courses of Tamiflu. More than 150 workers with potential exposure to the infected poultry received antiviral medication. State health officials promptly notified the CDC, allowing the agency to send a bilingual team to assist in the investigation.
Nahid Bhadelia, director of Boston University’s Center on Emerging Infectious Diseases, expressed concern about the virus potentially mutating to become more transmissible person-to-person and cause more severe illness.
“So far, the illnesses have not been severe,” she said. “But it’s only a matter of time before the disease may find someone with medical conditions that could make it more serious.”