CDC: Heat may have contributed to four human cases of bird flu in Colorado

Heat probably played a role in at least four cases of bird flu in poultry workers confirmed by U.S. health officials Sunday—the first cases in poultry workers in two years.

Sweltering temperatures in Colorado rose to at least 104 degrees, which is suspected to have contributed to the human cases, according to Dr. Nirav Shah, principal deputy director at the Centers for Disease Control and Prevention. The barns where poultry workers were culling chickens were "no doubt even hotter," Shah said during a press conference on the most recent outbreak of bird flu in humans.

The new cases bring the U.S. total to at least nine cases since the first human case of the current outbreak was detected in 2022, also in a Colorado poultry worker. Eight of the nine were reported this year.

The workers were separating chickens that were going to be killed to stop the spread of the virus. The fans may also have contributed to the human infections because, while helping to keep the environment cooler, they "also spread things like feathers around which are known to carry the virus," Shah added.

The large and strong fans also make it difficult for protective goggles and face masks to stay in place, he said.

About 60 workers at the poultry farm showed symptoms of illness and were tested for bird flu. Four tested positive for bird flu and one additional presumptive case is awaiting confirmation.

The illnesses were relatively mild, with symptoms including conjunctivitis and common respiratory infection symptoms like fever, chills, coughing, sore throat and runny nose, according to the CDC. None were hospitalized, officials said. The other U.S. cases have also been mild.

Officials said they are bracing for more cases.

The CDC says the risk to the general public remains low and the health agency is not recommending livestock workers be vaccinated against bird flu given the "mild symptoms noted thus far," Shah said.

An initial analysis of virus samples from an infected poultry worker does not show any changes in the virus that would make it easier to spread among people and there is no evidence of person-to-person spread in the U.S.

"It's important to note that this assessment is based on what we know today and may change," Shah said. "CDC is constantly looking for key changes that may alter our risk assessment of the virus, such as the severity of illness that it causes, the ease with which it can transmit to humans or changes to its genetic fingerprint."

At the request of Colorado's officials, the CDC sent a 10-person team to Colorado to help the state manage the bird flu outbreak in humans and poultry. The team included epidemiologists, veterinarians, clinicians and industrial hygienists.

Shah also noted it was a bilingual team. Overall in the U.S., it is estimated about half of farm workers are Latino.

An analysis of the virus from an infected worker indicates that the infections at the chicken farm are "largely the same" as the strain detected in dairy herds in Colorado and other states, according to Shah. But an investigation is ongoing to determine exactly how the outbreak is spreading between wild birds, chicken and cattle.

Since 2022, a highly contagious strain of bird flu has spread across the U.S. at an unprecedented rate.

Georgia's powerhouse poultry industry, which produces more broiler chickens than any other in the country, has mostly dodged the kinds of major outbreaks that have resulted in the deaths of more 90 million birds in commercial and backyard poultry flocks in the U.S.

About 1.8 million chickens will be killed at the Colorado poultry farm after these latest bird flu cases were detected.

In late 2023, ducks at a commercial breeding farm in Sumter County, Georgia, tested positive for H5N1. This year, in March, the virus made a jump to a mammal species that surprised many scientists: cows.

With a significant dairy industry, plus even larger beef and poultry interests, the potential arrival of the virus here threatens Georgia's economy and the health of residents.

As of Monday, the H5N1 virus has been confirmed in 158 dairy herds in 13 states, according U.S. Agriculture Department.

So far in Georgia, there have been no bird flu cases in cattle, and there have been no human cases.

Since the unprecedented spread of H5N1 in poultry in 2022, the Georgia Department of Public Health has quietly monitored 132 people for signs of the virus, according to DPH spokeswoman Nancy Nydam. Those tracked were either first responders to one of the state's few virus outbreaks in backyard and commercial poultry flocks or farmworkers where the infections occurred. Of those monitored, fewer than 10 people were tested for H5N1 and none came back positive.

Since the virus was discovered in cattle, a small number of first responders from Georgia who went to other states to help with investigations—fewer than 15—have also been monitored for signs of illness.

Federal officials said Tuesday they still believe they can eliminate the bird flu virus from dairy herds, even as the number of herds infected continues to grow. The latest state to recently report infected dairy cattle was Oklahoma. North Carolina is the only state adjacent to Georgia to report an infected dairy herd.

Eric Deeble, acting senior adviser for the H5N1 response at the USDA, said investigations show the virus is spreading among cattle through cattle moved from one herd to another and the shared use of milking equipment. It can be contained through enhanced biosecurity measures such as thoroughly cleaning milking "parlors" and equipment, separating sick cows, and having dairy workers wear protective equipment.

Deeble also noted USDA scientists are also working with partners to develop a cattle-specific H5N1 vaccine—a process requires many steps and will take time.

The USDA is also exploring the possibility of developing a poultry vaccine as the number of bird flu cases soar, and outbreaks lead to the slaughter of millions of farmed birds. But USDA and industry stakeholders point to challenges that would hinder a vaccination program.

The biggest sticking point is around trade.

Mike Giles, president of the Georgia Poultry Federation, said mass vaccination would be impractical for several reasons, including the fact that the industry would lose its lucrative export market: The United States and many of its trade partners restrict the import of poultry products or eggs from countries affected by the highly pathogenic strain or flocks that have been vaccinated against it.

"(Bird flu) has been, from an animal health standpoint, our top concern," Giles said. "The challenge, and I think the industry has responded to it well, has been maintaining the state of preparedness and urgency and focus on biosecurity, and I think that has been accomplished."

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