Colorado workers were exposed to bird flu while killing infected chickens, authorities say

Triple-digit temperatures, industrial fans and carts used to kill millions of sick chickens with gas may be the cause of the largest outbreak of bird flu among U.S. workers to date, U.S. health officials said.

Four workers at a commercial egg-laying facility in northeast Colorado have been confirmed to have bird flu, and another is presumed infected pending test results. The number of sick workers in Colorado, announced over the weekend, doubles the number of human cases in the U.S. since farmworkers began contracting bird flu this year, first in dairy cows.

Workers at the poultry farm in Weld County were in the process of killing 1.8 million chickens, some of which were infected with the dangerous H5N1 flu, to prevent its spread, federal officials said at a press conference on Tuesday.

Their goggles or N95 face masks apparently slipped as industrial fans blew feathers and other infected items through the sweltering barn, exposing them to the virus, said Dr. Nirav Shah, deputy director of the Centers for Disease Control and Prevention.

All of the workers suffered from a combination of fever, chills, cough and eye infections, Shah said. They were given the antiviral drug Tamiflu and none required hospitalization.

The risk of the virus to the general population remains low, Shah said. The workers' illnesses have been relatively mild, he said, and Tamiflu remains effective. And the virus's genetic sequence has not changed much since December, when the virus jumped from Texas to a dozen other states, including Colorado — and from birds to cows and then apparently back to chickens and finally to people.

“We have not seen any severe disease, which is reassuring,” Shah said. “In addition to the severity of the disease, we also look at whether the virus can be transmitted more easily or efficiently from animals to humans and/or from person to person. We have not seen any changes, especially from person to person.”

The evolving transmission route

Officials said they don't know exactly how the H5N1 virus got to the Weld County poultry farm. In early July, Colorado Gov. Jared Polis declared a disaster emergency after an outbreak occurred at the facility, the largest affected chicken flock in the state and one of the largest in the United States.

A few days earlier, a dairy worker, also in northeast Colorado, had become infected with bird flu. It was the first case in the state while working with infected cows.

Cattle in the same region of Colorado are known to be infected with the specific variant of the virus, so it is likely, although not yet confirmed, that the virus was transmitted from cattle to chickens, said Dr. Eric Deeble, acting senior adviser to the U.S. Department of Agriculture for the H5N1 response.

“Poultry is very susceptible and easily infected,” Deeble said in a phone call with reporters. “It doesn't take much to introduce this into a flock.”

Once poultry on a farm is infected with H5N1, the only way to contain the virus is to kill the entire flock, the U.S. Department of Agriculture said. Killing all 1.8 million chickens could take up to two weeks, Deeble said.

Hot barns, flying feathers

About 160 workers in the facility's barns were tasked with removing chickens and placing them several at a time on a cart that was then filled with carbon dioxide, killing the chickens in less than a minute and a half, Dr. Julie Gauthier, the USDA's executive director of field operations in the Animal and Plant Health Inspection Service, said in the call.

Temperatures have risen to 40 degrees in northeast Colorado, but Shah said it was even hotter inside the barns. Workers wore lightweight paper coveralls over their clothes, N95 respirators, goggles, boots and gloves. Industrial fans pumped air through the barns.

The fans made wearing PPE uncomfortable while feathers – a transmission route for the bird flu virus – flew around, likely causing the infections in five workers, officials said.

That suggests risks can be better controlled in the future through more systematic use of PPE and measures to improve ventilation, Shah said. A 10-person CDC team, including bilingual speakers and an industrial hygienist, arrived in Colorado on Saturday to monitor and test workers and suggest safety improvements.

A total of 60 workers were tested for bird flu, 55 of whom tested negative, but many of them showed symptoms consistent with other respiratory diseases such as rhinovirus, Shah said.

Sixteen workers who showed symptoms were tested Monday, AnneMarie Harper, a spokeswoman for the Colorado Department of Public Health and Environment, said in an email. Testing is still ongoing, and Shah said more infections could come to light.

This is what preparation looks like

Some of the virus found on the surface remained unchanged from the first infected person in Texas to the first infected person in Michigan to the workers recently sickened in Colorado, Shah said, suggesting the virus has not mutated and become more of a concern.

The Health Department's Strategic Preparedness and Response Agency is pushing ahead with production of millions of doses of bird flu vaccine by July to build a stockpile for the pandemic, said David Boucher, chief of the Infectious Diseases Agency's preparedness and response branch.

There is no recommendation yet for the administration of the vaccine to humans because the vaccine has not yet been fully tested or approved for use.

The agency also distributed 5,000 pairs of goggles, 300,000 gloves, 150,000 N95 masks and 528 doses of Tamiflu to Colorado, Boucher said.

“That's what preparation looks like,” Shah said. “It's making sure you have adequate supplies and supplies in case you need them, rather than trying to get them at the last minute.”

Contributors: Karen Weintraub

This article originally appeared on USA TODAY: Bird flu outbreak among poultry workers in Colorado doubles U.S. case count