The Colorado Department of Public Health and the Environment (CDPHE) reported Sunday that five workers have tested positive for the highly pathogenic avian influenza (H5N1 bird flu) virus. All five workers are employed by a single commercial egg layer operation. Thus, the event represents the first cluster of bird flu cases in humans, from a common source, discovered to date.

All the workers were involved in slaughtering chickens known to be infected with H5N1, a process known as culling. The workers were part of an effort to control the spread of the virus by culling 1.8 million chickens.

The Centers for Disease Control and Prevention (CDC) confirmed the test results for four of the five workers, with confirmatory testing currently in progress for the fifth individual. The CDPHE had reported “presumptive positive” results for three of the five on Friday, noting that samples had been sent to the CDC for the confirmatory testing. 

For the fourth CDC-confirmed positive worker, the state’s presumptive positive result came back late Friday evening and was confirmed by the CDC on Saturday. The fifth outstanding presumptive positive result occurred Saturday and samples were sent to the CDC for confirmation, which is pending.

“I am extremely concerned that we are on the brink of this being really already in humans—and once it’s in humans, it is going to be a real problem to control,” said Seema Lakdawala, an influenza specialist at Emory University.

The concern expressed is not only the occasional “spillover” case from animals to a human, although that type of event itself is highly worrying. Rather, the significant additional concern with this cluster of cases, arising from a single operation and in close temporal proximity, is that it raises the possibility that the virus has already gained the ability to transmit from human to human. 

“When it’s clustered like that, it tells you that your risk has gone way up because the contact is causing the illness,” said May Chu, an epidemiologist and professor at the Colorado School of Public Health. “The concentration of persons at one location getting infected tells me the virus is spreading a lot better.”

Colorado Governor Jared Polis had already declared a disaster emergency on July 5 in response to the outbreak in chickens in the Weld County facility at the center of the outbreak. This declaration activated the state’s Emergency Operations Plan to allow the Colorado Office of Emergency Management to provide resources to help the facility respond to and contain the bird flu outbreak.

The five infected persons had symptoms of conjunctivitis, an inflammation of the eye that gives it a pink or red appearance, and “common respiratory infection symptoms.” The reports do not indicate further which respiratory symptoms the workers were experiencing. Conjunctivitis has been reported in other human cases of H5N1 acquired from poultry and cattle, including one worker at a dairy farm in Colorado whose case was reported on July 3.

At present, the H5N1 virus spreads to humans through direct contact with infected animals or contaminated equipment such as cow milkers. Thus, the best way to prevent acquiring an H5N1 infection is to wear personal protective equipment such as masks, gowns, gloves, and goggles that serve as a barrier against infected material.

Neither the CDPHE nor any federal agency including the CDC, the Occupational Safety & Health Administration (OSHA), or the US Department of Agriculture (USDA), requires companies to provide PPE to workers or mandates the wearing of PPE during activity that brings workers into close contact with infected poultry or cattle. Instead, the CDPHE itself has been attempting to supply workers with the PPE necessary to protect themselves from the virus and urging workers to use it.

At the CDPHE’s invitation, the CDC has sent a team to Colorado to support the CDPHE’s investigation. Otherwise, the CDC has not yet taken any urgent action in response to this significant event. It has not changed its guidance on either PPE or the investigation of H5N1 bird flu.

Notably, there has been no major effort anywhere in the United States to expand surveillance and control of the virus commensurate with its pandemic potential. Since March, only 61 humans have even been tested for H5N1, according to the CDC. These numbers appear to omit the five individuals tested from the Colorado outbreak, since a July 10 web archive of the CDC H5N1 monitoring page reported 60 individuals tested.

No federal or state agency has done serological testing, which looks for antibodies to the virus in blood with the goal of understanding the overall levels of exposure in a community. Nor have they tested close personal contacts of those infected with H5N1, let alone the contacts of all individuals tested.

Also, nearly all current recommendations and guidance are optional. A federal order issued April 24 requires negative H5N1 testing results for all lactating dairy cattle prior to interstate shipment from one farm to another. Testing for all other types of cattle is not required. All recommendations regarding PPE and testing of humans for the virus are optional. No quarantine of infected humans is required.

Rick Bright, an immunologist and former federal health official, recommended such testing, saying “I’d like to see them swabbing from not just the symptomatic people that they’ve talked about, but also asymptomatic people on the same farm in the family circle unit and in the community.”

Lakdawala criticized the high degree of passivity of waiting for human-to-human transmission to occur rather than working actively to prevent it: “I will tell you that what has been driving me the past few months is trying to prevent H5 from becoming a pandemic. … I have never felt that we were as close as we are now.”

Bright additionally urged the federal government to make H5N1 vaccinations available to frontline poultry and dairy workers, saying, “It’s unethical to put farm workers on front lines to address the #H5N1 outbreak without the full protection available to them today.”

Such vaccinations could also substantially prevent the evolution of H5N1 in humans into variants that are capable of human-to-human transmission as well as subsequent actual transmission.

The federal and state agencies with the authority and technology to contain H5N1 and prevent it from becoming the next pandemic are not doing what is both within their means and required. Instead, beholden to the interests of the poultry and dairy industries, they are doing the absolute minimum possible consistent with not impacting profits. 

Even the lone mandate for testing lactating dairy cattle prior to interstate transport has failed to prevent outbreaks in dairy cattle in new states. The USDA just reported on July 15 that it had detected H5N1 in dairy cattle in Oklahoma for the first time, making it the 13th and latest state with the virus.