DENVER — The US Centers for Disease Control and Prevention (CDC) has not changed its stance on the risk level of highly pathogenic avian influenza (HPAI) to the public or its recommendations for poultry and dairy workers following recent reports of five positive cases in humans at a commercial egg layer operation.

CDC confirmed the presence of HPAI in four Colorado workers on July 14, along with a fifth presumptive positive case.

The outbreak marked the first human HPAI case in a poultry worker since the first and only other reported poultry worker case in 2022.

The five workers reported mild illness, with symptoms including conjunctivitis, eye tearing, fever, chills, coughing and sore throats. None have been hospitalized, and all were offered Tamiflu and are now recovering, said Nirav Shah, principal deputy director of the CDC, in a press call on July 16.

“CDC is not recommending H5-specific vaccines for livestock workers, given the mild symptoms that have been noted thus far and the absence of any changes to the virus’s genetic makeup that would suggest the risk to human health has increased,” he said.

Approximately 160 people were working on the site to depopulate the birds following the Colorado poultry farm outbreak, including producers, employees, contractors and US Department of Agriculture employees, said Julie Gauthier, executive director of field operations for the USDA’s Animal and Plant Health Inspection Service.

The CDC obtained samples from approximately 60 people on the farm who were symptomatic, which have all been processed, indicating that among those only five were positive for H5N1.

Shah commended the quick response of Colorado health and agriculture officials following the human cases.

Colorado officials were very proactive by requesting personal protective equipment (PPE) back in May, said David Boucher, director of infectious disease preparedness and response at the Administration for Strategic Preparedness and Response (ASPR). They requested 5,000 goggles, over 300,000 gloves and 150,000 N95 respirators.

In response to the current situation, Colorado requested Tamiflu that was overnighted.

“Understanding why an outbreak occurs at a particular time and place is a key question,” Shah said. “In this situation, environmental factors may have played a role.”

Namely, at the time that transmission is thought to have occurred, Colorado temperatures reached 104° F. Shah points out that the barns in which culling operations occur were likely even hotter, making PPE use a challenge. The facility used large-scale industrial fans to help keep the barn cool; however, those fans also spread feathers around, which are known to carry the virus.

Additionally, the culling method used involved workers moving from chicken to chicken, increasing potential interaction with an infected bird.

“PPE use was not optimal, particularly the masks and eye protection,” Shah said, adding that with the air movement from the fans, workers found it difficult to find a good seal for PPE.

The infected poultry farm is in a county where cows have also tested positive for H5N1, noted Eric Deeble, deputy undersecretary for marketing and regulatory programs at the US Department of Agriculture, on the call.

CDC’s investigation of the outbreak is ongoing.