Officials probe heat-wave factors in H5N1 spread to Colorado poultry cullers

As the investigation continues into recent avian flu infections in as many as five workers who culled Colorado poultry, officials today said that industrial fans in poultry barns where temperatures exceeded 104°F could have spread the virus through windblown feathers and through the air, potentially reducing the effectiveness of personal protective equipment (PPE).

Also, early genetic analysis suggests that the virus that infected the poultry and the workers is the same H5N1 genotype infecting dairy cattle, a useful clue for officials who are examining connections between the farms.

Quick response, bracing for more cases

So far, four H5 avian flu infections have been confirmed in cullers working at a large Colorado layer farm in Weld County that was hit by the virus. The Centers for Disease Control and Prevention (CDC) is working to confirm a fifth presumptive positive case.

At a Department of Health and Human Services (HHS) telebriefing today, Nirav Shah, MD, JD, principal deputy director for the CDC, said 60 workers with symptoms were tested, and so far only 5 tested positive in Colorado’s testing for H5 avian influenza. Others may be sick with other illnesses, such as rhinovirus. 

Shah praised Colorado health officials for their planning and preparedness. “As soon as there were symptomatic poultry workers, they sprang into action.” 

David Boucher, PhD, director of infectious disease preparedness and response at the HHS Administration for Strategic Preparedness and Response, said that, before the outbreaks, Colorado officials had obtained additional PPE from the Strategic National Stockpile (SNS), including goggles, gloves, and respirators. In the wake of infections in livestock workers, the state ordered and immediately received about 500 oseltamivir (Tamiflu) courses from the SNS.

Officials, however, are bracing for more cases, given the ongoing laborious culling process and challenges with the heat and PPE. 

PPE challenges in sweltering barns

Julie Gauthier, DVM, MPH, executive director for field operations with the US Department of Agriculture’s (USDA’s) Animal and Plant Health Inspection Service, said there are roughly 160 people involved in the culling process, and those who have hands-on roles wear Tyvek suits, N95 respirators, goggles, boots, and gloves. She said it’s possible that the hard push from the industrial fans may make it hard for workers to keep their goggles and respirators in place.

She said culling is a laborious process that requires workers to load several dozen chickens onto carbon dioxide gas carts, which kills the birds within about 90 seconds. The layer farm houses about 1.8 million birds, and officials expect the culling operation to be completed over the next 10 to 14 days.

Shah said a confluence of factors may have contributed to the farm worker infections and that the investigation is still under way. He added that a CDC environmental hygienist is part of the field team and is looking at ways to optimize PPE use and reduce the risk from environmental factors.

Eric Deeble, DVM, acting senior adviser for highly pathogenic avian influenza at the USDA, told reporters that it’s important for depopulation activities to continue, and that, if they are paused, workers would still be exposed to the H5N1 while caring for the surviving birds.

Symptoms vary in infected workers

So far, all of the H5N1-infected workers have mild infections and are recovering, Shah said. Though the CDC said earlier that the patients’ symptoms include conjunctivitis and typical flu symptoms, he emphasized that not all workers had respiratory symptoms and not all had eye symptoms.

No other illnesses have been found in patient contacts, he said. The workers are contractors who specialize in depopulation and have close connections at work as well as in their living situations, which Shah said makes contact tracing a bit easier for state health officials.

So far, there is no sign that the virus is more severe or more transmissible, either from animals to people or among humans, he said. The virus still remains avian, with no changes to make it better adapted to mammals. For now, Shah said H5 vaccine use isn’t indicated, though officials continue to closely assess the situation.

USDA field team on site

Deeble told reporters that a four-person trace-back team is on site to conduct the epidemiologic investigation on the animal side. They will explore how the poultry contracted the B3.13 genotype virus from cows. 

Weld County, where the layer farm is located, has been a hot spot for dairy farm H5N1 outbreaks in Colorado. Deeble said poultry are very susceptible to the H5N1 virus. “It doesn’t take much to introduce it into a flock.”

He said officials still have high hopes for eliminating the virus in dairy cattle, with good biosecurity and good farmer participation. Deeble said officials aren’t seeing any change in the pattern of spread. “The virus moves with the cattle and the people associated with them.”