CDC: Bird flu infections going undetected in farm workers
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Key takeaways:
- Seven percent of dairy farm workers in two states showed evidence of recent bird flu infection.
- The CDC recommended increases testing and treatment of asymptomatic people to stem the spread.
Seven percent of dairy farm workers in two states had evidence of a recent infection with highly pathogenic avian influenza, according to a new report published Thursday.
CDC officials said during a media telebriefing that the agency is recommending increased testing of farm workers nationally and that anyone who tests positive be treated with the antiviral oseltamivir even if they are asymptomatic, based on the serology data showing there have likely been more human bird flu cases than reported.
“For clarity, there is nothing that we’ve seen in the new serology data that gives rise to a concern about person-to-person transmission,” CDC Principal Deputy Director Nirav D. Shah, MD, JD, said during the telebriefing. “This is fundamentally a respiratory virus, and although we have not seen changes to the virus that would suggest the capacity for it to spread from person-to-person, we want to keep that risk as low as it is right now.”
“One of the best ways to do that is to identify individuals who have been exposed through greater testing and provide them with [oseltamivir] to drive down the levels of virus in their body, which helps us keep that risk as low as possible,” Shah added.
Data presented during the telebriefing and published in MMWR shows that more people than previously thought have been exposed to and possibly infected with H5N1 at dairy farms and during bird culling in flocks where the virus has been detected.
In addition to data on unreported infections — the CDC is not calling evidence of infection detected in serological testing a “case” — a second MMWR study on Thursday showed that although personal protective equipment (PPE) use at farms where H5N1 has been detected has risen, it is not being used universally.
As of Nov. 6, the CDC has confirmed 46 H5N1 cases in humans since April, with cases in California climbing rapidly in the last 2 weeks to 21, all among dairy cattle workers. Twenty cases nationally were linked to poultry depopulation. The number of states reporting new outbreaks among birds or dairy herds, however, has dropped in the last 30 days from 14 to 2.
Overall, more than 105 million wild birds, poultry and backyard flocks have been affected by bird flu in 48 states, as have 443 dairy herds in 14 states, according to the CDC.
Eight infected dairy farm workers
According to the first study, researchers collected anonymized serum samples and conducted interviews with 115 dairy farm workers in Michigan (45) and Colorado (70) between June and August. They found that eight (7%) had evidence of H5N1 infection, whereas 78 (66%) had neutralizing antibodies against seasonal influenza from either vaccination or infection.
Among the workers with positive serology, 100% reported cleaning the milking parlor and 88% reported milking cows compared with 38% of those with negative serology cleaning the milking parlor and 57% milking cows, according to the study.
Overall, 46 workers (40%) reported feeling ill either shortly before or after H5N1 had been confirmed in cows on the farm. Four of the eight people with serologic evidence of infection reported red, draining or itching eyes, as did 64% of workers who reported they got sick but had negative serology for H5N1.
PPE use low
For the other study, researchers interviewed 83 dairy farm workers between July and August about their jobs on farms, whether they had felt ill or reported illness and about the use of PPE on the farms to protect workers from bird flu infection.
Workers reported either milking cows or working in the milking parlor (51%), cleaning cow manure (49%) and transporting cows (49%), and more than half (53%) reported exposure to infected cows a week before the virus was detected on the farm.
Workers reported that they were given gloves (88%), eye protection (76%), rubber boots or boot covers (71%) and head covers (69%) relatively regularly but that just 26% used N95 respirators, although the study notes that PPE use increased by about 28% after bird flu was detected and eye protection increased by 40% by workers milking cows.
During the telebriefing, officials said they are working with farms to increase the use of PPE to better protect workers and limit the spread of H5N1 from animals to humans, as well as to decrease the risk for human-to-human transmission.
In addition to increasing testing and treatment for people who test positive, the CDC is working with the NIH to determine if rapid home test kits for seasonal influenza or COVID-19 can effectively detect H5N1 in an effort to make it easier for people with mild illness to test more quickly.
“We know that there are individuals who may have been exposed or may have been infected that are not part of the count,” Shah said. “This is what serology data help us get a better retrospective understanding of, and we still need more data to better characterize that.”
“But better characterizing right now, how much of the iceberg is above the water versus below the water — it’s not something we have enough data on quite yet,” he said.
References:
- CDC. Bird flu: H5 bird flu: Current situation. https://www.cdc.gov/bird-flu/situation-summary/index.html. Updated Nov. 6, 2024. Accessed Nov. 7, 2024.
- Marshall KE, et al. MMWR Morb Mortal Wkly Rep. 2024;doi:10.15585/mm7344a2.
- Mellis AM, et al. MMWR Morb Mortal Wkly Rep. 2024;doi:10.15585/mm7344a3.
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