Colorado bird flu cases show how extreme heat may be complicating efforts to control the virus

“At the time transmission is thought to have occurred, Colorado was experiencing 104-plus-degree heat,” and it was probably hotter inside the barns, said Dr. Nirav Shah, principal deputy director of the US Centers for Disease Control and Prevention. The CDC is investigating the outbreak along with the Colorado Department of Public Health and Environment.

This made the use of personal protective equipment a challenge, Shah said.

In addition, to bring down temperatures in the sweltering barns, large industrial fans were blowing, moving air as well as dust and feathers. Feathers from infected birds are known to carry the H5N1 virus.

“We understand those large fans ... were moving so much air ... the workers were finding it hard to maintain a good seal or a good fit either between the mask or with eye protection,” Shah said.

Four of the Colorado cases have been confirmed by the CDC. A fifth tested positive at a state lab and has been sent to the CDC for confirmation.

The incident has quickly doubled the number of farm workers known to be infected with H5N1 virus in the United States, and it is the largest number of workers known to be infected in connection with a single farm.

In 2022, a poultry worker tested positive for H5N1 in Colorado. This year, four other farm workers have tested positive — one in Texas, two in Michigan and another in Colorado — after working with infected dairy cattle. Cases are believed to be undercounted because farm workers are often reluctant to be tested for fear of losing work and income.

Genetic analysis of the virus from one of the recent human cases involved in the poultry culling was reassuring, Shah said, because it didn’t show any mutations that might indicate the virus is spreading more readily to people. Testing also showed that the virus was closely related to the strain spreading in cattle.

At the state of Colorado’s request, the CDC has sent a 10-person team to assist with the investigation and contact tracing in the outbreak. Sixty people have shown symptoms consistent with bird flu, and all but five have tested negative at a state laboratory, Shah said.

“We’ve seen strong uptake of testing across this particular farm in Colorado,” he added.

None of the workers was hospitalized, and many had traditional flu symptoms, including conjunctivitis or eye infections, fever, chills, coughing and sore throats. The workers have been offered an antiviral medication and are recovering.

Altogether, about 160 people are involved in the culling, or killing, of 1.8 million egg-laying chickens on the Colorado farm, which is a “significant” egg-producing operation that officials didn’t name. The culling operation is expected to continue another 10 to 14 days.

It is not clear how the birds became infected, but viruses isolated from the birds are closely related to the same strain that’s infecting dairy cattle, said Dr. Eric Deeble, the US Department of Agriculture’s acting senior adviser of the H5N1 response.

The CDC maintains that the threat to the public of the H5N1 bird flu virus is low.

However, farm workers are at higher risk of catching the infection, which has recently spread from domestic and wild birds to dairy cattle and other mammals.

To stay safe, the CDC recommends that people working with sick or dead cattle or birds wear personal protective equipment, or PPE, which includes waterproof coveralls, a face mask, goggles or a face shield, boots, gloves and a head covering.

Workers involved in the culling of the chickens in Colorado were required to wear the full uniform, but environmental conditions made it difficult to keep on. “We understand that PPE use was not optimal, particularly the masks and the eye protection,” Shah said.

The United Farm Workers labor union has questioned whether the CDC’s recommendations are practical given the record-breaking heat enveloping much of the United States this summer. It had called on the CDC to rethink its PPE guidance so more people could follow it.

“These are people that are being asked to put their lives on the line for a virus we don’t understand all that well when they have no reasonable way of protecting themselves from either the virus or from heat illness,” Elizabeth Strater, director of strategic campaigns for United Farm Workers, said Tuesday. “They’re being put in an impossible position.”

Workers wear fluid-proof coveralls, Strater points out, which prevent sweat from cooling their bodies, making it easy to overheat. In dirty, wet environments like a barn, masks and respirators can become clogged or soggy within minutes.

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The CDC said it is working to refine its PPE recommendations to account for the heat. “We’ve sent, as part of our team, a specialist in these matters, an industrial hygienist who can help implement improved engineering controls that may make PPE use more uniform as well as more palatable,” Shah said.

Strater said it’s time for the CDC to consider vaccinating farmworkers, as Finland is, to give them – and the general public – an added layer of protection from the virus and from the threat of another pandemic if it spreads.

“They need to be prioritized, not just because it’s moral to protect their lives by prioritizing vaccination, but it’s a relatively small group of people, when you think about the sort of firewall they’re creating around the rest of the general public,” she said. “This is not a huge number of people we need to be protecting. These are people who are on the front lines and who are so intimately exposed.”

Although US health officials have stressed that they have no plans to distribute an H5N1 vaccine, they are getting several candidates ready to be deployed in case the virus becomes more dangerous.

In May, the US Department of Health and Human Services announced that it was ordering 4.8 million doses of H5N1 vaccine to be manufactured from bulk ingredients in the country’s Strategic National Stockpile. Those doses are expected to be ready by the end of the month.

In early July, HHS announced that it had paid Moderna $176 million to support the development of an mRNA-based vaccine against H5N1. The agency said it expects to see phase 1 clinical trial results on the safety of that vaccine by the end of the year.

The challenging environmental conditions, including hot temperatures and the use of large industrial fans, made it difficult for the workers to maintain proper use of personal protective equipment, such as masks and eye protection, as recommended by the CDC. Despite these challenges, the CDC advises that individuals working with sick or dead cattle or birds should wear personal protective equipment to stay safe, as they are at a higher risk of contracting the H5N1 bird flu virus.