Mild cases of bird flu in the US trigger safety warnings for the poultry and dairy sectors

Mild cases of bird flu in the US trigger safety warnings for the poultry and dairy sectors

Mild flu cases among US poultry and dairy workers spark warnings - why protective equipment and vigilance are important to stop outbreaks.

In a recent study published inThe New England Journal of MedicineResearchers analyzed eight months (March-October 2024) of United States (US) public health surveillance data to identify trends in influenza A(H5N1) cases among adults. They report 46 cases of bird flu infections in six states, all of which were mild and only one required hospitalization.

Specifically, 20 patients had contact with infected poultry, 25 with infected cows, and one with no identifiable source of exposure. Direct transmission from person to person could not be determined. The study results show that there is low compliance with the use of personal protective equipment (PPE). Only 36% of workers reported using 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 in Asia, Europe, Africa and the Middle East, resulting in significant economic and agricultural impacts.

Influenza A(H5N1) is the general medical term for a cohort of highly infectious influenza viruses (“flu viruses”) that cause severe respiratory diseases in birds (hence the colloquial name “bird flu”). Like most influenza viruses, H5N1 strains evolve extremely rapidly, with some having crossed class boundaries and are known to infect mammals (including humans).

A single human infection was first reported in Hong Kong in 1997, but between 2003 and 2024 alone, over 900 human infections were documented in 24 countries. Worryingly, while half of reported human infections are mild and do not require hospitalization, some can be serious - the cumulative mortality rate for H5N1 is 50%.

While human-to-human transmission is rare and remains absent in the United States of America (U.S.), cow-to-human transmission was reported in March 2024, prompting additional public health surveillance among poultry and dairy workers. The median age of the identified US patients was 34 years, with 80% being male. Elucidating the risk of transmission 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: For those with symptom resolution data, the median duration of illness was 4 days, with a range of 1 to 8 days.

The present study summarizes A(H5N1) cases diagnosed between March and October 2024 from state and local health surveillance data in the United States. It focuses on the potential occupational hazards in the poultry or dairy industry and highlights the use and importance of personal protective equipment (PPE) among these individuals.

Study data were obtained from public health officials monitoring occupationally exposed individuals (close contact with poultry or dairy cattle in the past 10 days) who exhibited H5N1 symptoms (mainly acute respiratory illness). Identified individuals were screened for the virus using nasopharyngeal swabs, combined nasal-oropharyngeal swabs, or conjunctival swabs.

Influenza A(H5N1) infections were confirmed using the Centers for Disease Control and Prevention (CDC) Human Influenza Virus Real-Time Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) Diagnostic Panel Influenza A(H5). Subtyping test." Conjunctival swabs detected the virus in 88% of symptomatic cases, while nasopharyngeal and nasopharyngeal swabs had lower detection rates. Samples from patients in whom H5N1 was detected were then transferred to CDC laboratories for real-time PCR and genetic sequencing analyses.

Study results

Comparing Symptoms by Exposure: Poultry workers reported fever (60%) and respiratory symptoms (45%) more frequently than dairy workers (40% and 28%, respectively).

The study identified 46 U.S. adults with confirmed H5N1 infections between March and October 2024. The patients were predominantly poultry and dairy workers exposed to infected animals, with 20 directly exposed to poultry, 25 exposed to dairy cows or raw milk, and one patient not exposed to contact with infected animals, with no identified source of exposure. The source of H5N1 in the final patient could not be determined, but human-to-human transmission was ruled out.

Encouragingly, the majority of the 46 patients identified reported mild symptoms that did not require hospitalization. These symptoms included conjunctivitis (~93%), fever (49%), and respiratory illness (36%). The only patient requiring hospitalization was the one with no identified source of infection who was hospitalized for three days with non-respiratory symptoms. No serious infections or H5N1-associated mortality have been documented across the United States. Treatment with oseltamivir (approximately 5 days) was sufficient to treat the disease in all documented patients.

Worryingly, access to and compliance with PPE use among occupationally exposed individuals was found to be severely lacking, with only 36% of workers wearing gloves, eye protection or face masks. Of these, 71% used gloves, 60% used eye protection, and only 47% used face masks, which may account for the high prevalence of conjunctivitis in identified patients.

Conclusions

The present study describes the incidence of influenza A(H5N1) in U.S. adults (median age: 34 years; predominantly male) and highlights that the disease almost exclusively affects poultry or dairy workers (n = 45). It highlights the occupational risks associated with these professions and identifies suboptimal use of PPE in this vulnerable cohort as a primary cause of escalating H5N1 cases in the country.

Although all identified cases were mild, the study warns that constant vigilance is needed to prevent potentially serious outbreaks. Improved education, systematic access to PPE and timely public health interventions could help protect poultry and dairy workers from an impending epidemic and should be prioritized by the health system.

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