At a glance
A new report included this week in CDC's Morbidity and Mortality Weekly Report (MMWR) focused on a study that assessed levels of antibodies against H5N1 virus in blood samples of dairy farm workers (i.e. a serologic study) and provides updated insights into the degree to which they have been exposed to H5N1 bird flu during this year's outbreak.
What to Know From This Report
In this week's Spotlight, we include the key findings from a recent study coordinated with state health departments in Michigan and Colorado, published in this week's MMWR. This study, also called a serosurvey, tests blood from people with exposure to dairy cows with H5N1 infection in order to determine if the workers had developed antibodies against the virus. This can help us better understand how frequently farm workers who are exposed to infected dairy cows may become infected with H5N1.
One hundred and fifteen people who worked on farms with cows infected with H5N1 participated in this study. Eight of these 115 people (7% of participants) showed evidence of recent H5N1 virus infection, and four of the eight with evidence of infection did not remember feeling sick or showing symptoms.
This study adds to the data CDC reported in July, which describe early results of the first phase of the study among 35 workers in Michigan. In that group of workers, none showed evidence of prior H5N1 virus infection. Eighty more workers were included in the second phase of this study in both Michigan and Colorado. Identifying some workers who did not recall feeling sick, but who had evidence of recent H5N1 virus infection, is important new data that informs new guidance to protect workers.
What CDC is Doing With These Findings
The risk of infection with H5N1 virus among the general public remains low.
However, these new findings highlight the need for employers and public health to strengthen prevention activities to better protect farm workers from this infection. Doing so is important to reduce the risk of H5N1 virus spread to exposed workers from sick animals.
Data generated by CDC, state and local public health, and animal health partners during this animal outbreak have shown that there are two primary ways that workers in the United States have been infected with H5N1 virus: via exposure to infected poultry during culling activities, and through exposure to infected dairy cows, including while caring for sick cows, or when working in a milking parlor, the area on the farm where cows are milked.
Based on these data, CDC is updating its existing recommendations on actions to prevent exposures to H5N1 infected animals. These enhanced actions include:
- Decreasing human exposure through One Health control strategies and biosecurity to limit H5N1 virus infections in animals.
- Enhancing personal protective equipment (PPE) guidance to more clearly detail what PPE is appropriate for exposure risk levels (high, medium, and low) in farming and poultry culling operations, alongside more robust worker training on proper use of PPE.
- Identifying exposed workers and providing appropriate testing as well as post-exposure prophylaxis (i.e., efforts to limit spread of disease), and treatment (e.g., antivirals).
- Offering testing to asymptomatic workers with a high-risk exposure who reported not wearing relevant PPE or who experienced a PPE breach or failure.
- Increasing outreach and education with farm workers, employers, and advocacy groups to stress and ensure understanding of these messages and strategies.
Working with its partners, CDC has updated its existing H5N1 guidance to employers and workers to provide recommendations for measures that can be taken to prevent animal-to-human transmission of H5N1. Data from the serosurvey and case investigations have identified settings and activities that are higher risk for transmission of H5N1, allowing CDC to better prioritize its PPE recommendations. In this update, CDC has tailored its PPE recommendations to match the risk of H5N1 exposure during different work tasks and in different settings to better protect workers againstH5N1 infection from sick animals. The updated PPE guidance helps employers and workers prioritize what PPE is used in settings associated with high and moderate-risk exposures and also defines situations where higher levels of PPE may not be needed.
CDC has also updated its recommendations for testing and for offering oral antiviral medications such as post-exposure prophylaxis for asymptomatic workers who report a high-risk exposure to animals with H5N1. These updates recommend that asymptomatic workers with a PPE-unprotected, high-risk exposure to sick animals be offered oseltamivir, an FDA approved oral influenza antiviral, for post-exposure prophylaxis of H5N1. As a reminder, oseltamivir may be used to treat people with an H5N1 infection, and be given after an exposure to influenza to prevent infection, also called post-exposure prophylaxis or PEP. A high-risk exposure could include an unprotected splash in the face with raw cow milk from an infected or potentially infected cow, or not using recommended PPE during activities to depopulate poultry at a poultry farm with known H5N1. Also, the recommendations include offering influenza A(H5) testing to asymptomatic workers who had a high-risk exposure to animals with H5N1 whether the worker decides to begin PEP or not.
CDC continues to recommend that people who have been exposed to animals infected or potentially infected with avian influenza A(H5N1) viruses should watch for symptoms, even very mild symptoms, such as eye irritation, and seek testing and care as soon as possible if symptoms develop.
CDC will continue to work with local, state and Federal partners, the National Center for Farmworker Health, as well as foundations and associations who support local agricultural extensions, to help these organizations inform farm workers about H5N1 and how to protect themselves from this infection. Additional outreach will focus on key worker and employer groups as well as advocacy groups for Latino populations, such as the National Alliance for Hispanic Health, the National Hispanic Medical Association, and UNIDOS, to alert these organizations to these updated strategies to support farm worker health.
A Note About the Importance of Seasonal Flu Vaccination and the H5N1 Outbreak
As we enter our annual flu season, CDC is working closely with partners to ensure farm workers have access to seasonal flu vaccine. While the seasonal flu vaccine does not protect against infection with H5N1, expanding access to seasonal flu vaccines among farm workers can lower their risk of developing severe illness related to seasonal flu and limit the spread of seasonal flu among this group. CDC currently recommends that all people 6 months and older get their flu shot to help prevent flu and its complications.