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Mild flu cases in US poultry and dairy workers spark warnings—why protective gear and vigilance matter in stopping outbreaks. Study: Highly Pathogenic Avian Influenza A(H5N1) Virus Infections in Humans . Image Credit: Nataliia Maksymenko / Shutterstock In a recent study published in The New England Journal of Medicine , researchers analyzed eight months (March-October 2024) of United States (US) public health surveillance data to identify trends in adult influenza A(H5N1) cases.
They report 46 cases of avian influenza infection across six states, all of which were mild, and only one of which required hospitalization. Notably, 20 patients had contact with infected poultry, 25 with infected cows, and one with no identifiable exposure source. No direct human-to-human transmission could be established.
Study findings reveal low adherence to personal protective equipment (PPE) use, with only 36% of workers reporting the use of gloves, eye protection, or face masks. This highlights the need for improved PPE dissemination, education, and prompt testing/treatment in this vulnerable population. Background Global spread among bird populations: Since its emergence, H5N1 has caused outbreaks in bird populations across Asia, Europe, Africa, and the Middle East, leading to significant economic and agricultural impacts.
Influenza A(H5N1) is the medical umbrella term for a cohort of highly infectious influenza (‘flu’) viruses causing severe respiratory diseases in birds (the source of their colloquial name “bird flu”). Like most influenza viruses, H5N1 strains evolve at extremely rapid paces, with some having crossed over class barriers and known to infect mammals (including humans). First reported in humans from a single infection in Hong Kong (1997), over 900 human infections across 24 countries have been documented between 2003 and 2024 alone.
Alarmingly, while half of reported human infections are mild and require no hospitalization, some can be severe—the cumulative fatality rate of H5N1 is 50%. While human-to-human transmissions are rare and remain absent in the United States of America (US), a cow-to-human transmission was reported in March 2024, prompting additional public health surveillance among poultry and dairy workers. The median age of identified US patients was 34 years, with 80% being male.
Elucidating transmission risk in this potentially vulnerable cohort would provide clinicians and policymakers with the information necessary to prevent or contain potential disease outbreaks. About the Study Duration of illness: Among individuals with symptom resolution data, the median illness duration was 4 days, ranging from 1 to 8 days. The present study summarizes US state and local public health surveillance data-derived A(H5N1) cases diagnosed between March and October 2024.
It focuses on the potential occupational hazards of poultry or dairy farming and highlights the use and importance of personal protective equipment (PPE) among these individuals. Study data was obtained from public health officials who monitored persons occupationally exposed (close contact with poultry or dairy animals in the preceding 10 days) depicting H5N1 symptoms (mainly acute respiratory illness). Identified individuals were screened for the virus via nasopharyngeal swabs, combined nasal–oropharyngeal swabs, or conjunctival swabs.
Influenza A(H5N1) infections were confirmed via the use of the ‘Centers for Disease Control and Prevention (CDC) Human Influenza Virus Real-Time RT-PCR (reverse-transcriptase–polymerase-chain-reaction) Diagnostic Panel Influenza A(H5) Subtyping assay’. Conjunctival swabs detected the virus in 88% of symptomatic cases, while nasopharyngeal and nasal–oropharyngeal swabs showed lower detection rates. Samples from patients with H5N1 detected were then transferred to CDC laboratories for real-time PCR and genetic sequencing analyses.
Study Findings Symptoms comparison by exposure: Poultry workers were more likely to report fever (60%) and respiratory symptoms (45%) compared to dairy workers (40% and 28%, respectively). The study identified 46 adult US citizens with confirmed H5N1 infections between March and October 2024. Patients were predominantly poultry and dairy workers exposed to infected animals, with 20 having direct poultry exposure, 25 exposed to dairy cows or raw milk, and one patient with no identified exposure source.
The source of H5N1 in the final patient could not be determined, but human-to-human transmission was ruled out. Encouragingly, of the 46 patients identified, the majority reported mild symptoms not requiring hospitalization. These symptoms included conjunctivitis (~93%), fevers (49%), and respiratory ailments (36%).
The only patient requiring hospitalization was the one without an identified infection source, who was hospitalized for three days with non-respiratory symptoms. No severe infections or H5N1-associated mortality were documented across the US. Oseltamivir treatment (~5 days) was sufficient to treat the condition in all documented patients.
Alarmingly, access and adherence to PPE use in occupationally exposed individuals was found to be severely lacking, with only 36% of workers using gloves, eye protection, or face masks. Among these, 71% used gloves, 60% used eye protection, and only 47% used face masks, potentially accounting for the high prevalence of conjunctivitis among identified patients. Conclusions The present study describes the incidence of influenza A(H5N1) among adult US citizens (median age: 34 years; predominantly male) and highlights the disease’s almost exclusive infection of poultry or dairy workers (n = 45).
It underscores the occupational hazards associated with these professions and identifies the suboptimal use of PPE within this vulnerable cohort as a key contributor to escalating H5N1 cases within the country. While all identified cases were mild, the study warns that ongoing vigilance is required to prevent potentially severe outbreaks. Improved education, systematic PPE access, and timely public health interventions could help protect poultry and dairy workers from an impending epidemic and should be prioritized by the healthcare system.
Garg, S., Reinhart, K., Couture, A.
, Kniss, K., Davis, C. T.
, Kirby, M. K., Murray, E.
L., Zhu, S., Kraushaar, V.
, Wadford, D. A., Drehoff, C.
, Kohnen, A., Owen, M., Morse, J.
, Eckel, S., Goswitz, J., Turabelidze, G.
, Krager, S., Unutzer, A., .
.. Olsen, S.
J. (2024). Highly Pathogenic Avian Influenza A(H5N1) Virus Infections in Humans.
In New England Journal of Medicine . Massachusetts Medical Society, DOI: 10.1056/nejmoa2414610, https://www.
nejm.org/doi/full/10.1056/NEJMoa2414610.
