Two Colorado chicken farmers infected with bird flu, one at second farm

The Colorado Department of Public Health and Environment (CDPHE) announced today, just days after the new cases were reported at the first poultry farm, that another worker slaughtering poultry at a second large poultry farm has preliminary tested positive for H5N1 avian influenza, bringing the total number of cases to seven.

Additionally, the Centers for Disease Control and Prevention (CDC) confirmed initial positive H5N1 results in two recent cases in Colorado, provided details of the genetic sequencing of samples taken from infected poultry cullers in Colorado, and reported preliminary results from a seroprevalence survey of farmworkers in Michigan.

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in statement CDPHE announced today that the state's initial positive test patient was providing support at a second large egg farm in Weld County affected by the virus. The two large egg farms, which together house approximately 3 million chickens, are undergoing culling efforts.

Federal health officials said last week that culling workers are working in sweltering heat at chicken farms, which could reduce the effectiveness of their personal protective equipment and further spread environmental contamination, and that culling chickens is a time-consuming and labor-intensive process that involves manual labor, increasing workers' exposure to the virus.

July 19 statementCDPHE reported that an additional case had been confirmed in the first of two chicken farms previously reported to be infected. update The CDC said it had confirmed the H5N1 virus in the two recent cases at the first farm, adding that as in the earlier cases, the workers had mild infections and were given the antiviral drug oseltamivir.

The CDC also said it has uploaded the genetic sequence of the virus from one of the Colorado cull companies to a public database. It is closely related to the B3.13 genotype found in recent poultry outbreaks and infected cattle herds. “This is the only virus that CDC has been able to fully sequence from a Colorado case to date,” the group said.

The virus has primarily avian genetic characteristics and does not possess mutations that enhance its ability to infect or spread to humans. It possesses the same PB2 M631L mammalian adaptation marker as seen in nearly all dairy cow genetic sequences and the first human cases in Michigan. The PB2 E627K mutation, previously associated with mammalian adaptation, was not seen in previous human cases in Texas.

Early data suggests asymptomatic transmission is unlikely

In its update, the CDC also detailed early results from a Michigan-led seroprevalence study that looked at blood samples from 35 people who work on Michigan farms where the H5N1 virus outbreak has occurred in dairy cows so far in June. Participants came from multiple counties and had different roles, but all had direct experience working with sick cows. Fewer than half reported wearing masks or goggles.

The researchers tested blood samples for antibodies to the H5N1 lineage 2.3.4.4b virus, which could indicate undetected infection. As a control, they also measured antibodies to seasonal influenza viruses. None of the 35 workers had antibodies to H5N1, but many had neutralizing antibodies to seasonal influenza, suggesting previous infection or vaccination.

The CDC said the initial findings are consistent with previous studies in Asia that suggested low seroprevalence of H5N1, even among known infected workers.

The Michigan Department of Health and Human Services is continuing its investigation and will be working with the CDC to analyze the data and submit the results for peer-reviewed publication. The CDC is also working with the American Association of Bovine Veterinarians to conduct a seroprevalence survey of cattle veterinarians, which it expects to conduct within the next two months.

The number of infected dairy farms continues to rise, with five new outbreaks confirmed, bringing the national total to 168 across 13 states, according to the latest report. update According to the United States Department of Agriculture's Animal and Plant Health Inspection Service (APHIS), four of the latest confirmed cases were in Colorado and the fifth in Minnesota.