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<h2>What to Know</h2>
In this week's spotlight, the CDC has unveiled a range of new resources specifically designed for employers of farm workers. These resources address health safety and vaccination protocols to mitigate risks related to avian influenza. Additionally, the CDC shared insights from a recent radio media tour conducted for journalists, which emphasized critical information regarding the circulating flu strains. Noteworthy findings also emerged from the genetic sequencing of avian influenza A(H5) viruses, particularly relating to recent human cases in Washington and California after exposure to infected animals.
<h2>Situation Update</h2>
November 18, 2024 – The CDC is actively addressing the public health concerns associated with a troubling multistate outbreak of avian influenza A(H5N1) virus, commonly referred to as "H5N1 bird flu." This outbreak has been identified across various species, including dairy cows and poultry, throughout the United States. In collaboration with the U.S. Department of Agriculture (USDA), the Food and Drug Administration (FDA), and the Administration for Strategic Preparedness and Response (ASPR), the CDC is employing a comprehensive One Health approach, which links human, animal, and environmental health.
So far, health officials have reported a total of 52 confirmed cases across multiple states. Among these, 26 cases have been identified in dairy farm workers in California, with five of these cases confirmed by the CDC on November 13 and 14. Additionally, a confirmed case was detected in a poultry farm worker from Oregon, marking the first instance of H5N1 bird flu in the state. All recorded cases have been linked to workers on farms that have been significantly impacted by the outbreak. Evidence suggests that these instances represent isolated cases of animal-to-human transmission. The farm workers involved have generally experienced mild symptoms, predominantly manifested as conjunctivitis, characterized by redness or discharge from the eyes. Some individuals tested positive in Washington reported having mild upper respiratory symptoms, but critically, none required hospitalization.
The CDC is closely monitoring an additional human case of H5N1 bird flu that has been reported in Canada. They are in communication with the Public Health Agency of Canada (PHAC), which has confirmed that this case is associated with a variant of H5N1 virus distinct from those affecting animals in the U.S. Detailed information regarding this Canadian case, along with the continuing epidemiological investigations, has been made available through a public statement by PHAC. For an up-to-date overview of case counts in the United States, CDC provides a detailed table on their website, categorizing data by state and source of exposure. Importantly, no evidence of person-to-person transmission of H5 bird flu has been observed within the U.S. CDC maintains that the immediate risk to the general public remains low; however, individuals with direct exposure to infected animals face a heightened risk of infection.
From an animal health perspective, the USDA has confirmed instances of infected cattle in a staggering 505 dairy herds across 15 states since March 2024. The spread of the virus has shown an upward trend, with new infections primarily concentrated in California. Furthermore, the USDA reports that H5 has been detected in 50 commercial poultry flocks and 38 backyard flocks since April 2024, collectively impacting approximately 25.61 million birds across the country.
<h2>Laboratory Update</h2>
To date, the CDC has confirmed a total of 11 human cases of H5 bird flu in poultry farm workers located in Washington state. Genetic sequencing conducted on clinical specimens from these cases revealed no significant changes in the hemagglutinin (HA) component that would suggest increased infectivity or transmissibility among humans. Nonetheless, CDC identified a notable alteration, termed NA-S247N, in the influenza specimens from three of the H5 cases. This change may confer a marginal reduction in susceptibility to oseltamivir, a neuraminidase inhibitor, based on laboratory tests. The NA-S247N change has previously been observed sporadically in seasonal influenza viruses and has rarely been reported in A(H5N1) strains. Historically, tests conducted on two A(H5N1) viruses—one sourced from a chicken in Laos in 2008 and another collected from a dolphin in Florida in 2022—showed varying degrees of reduced inhibition by oseltamivir, but results remained considerably lower than those indicating resistance noted in other influenza viruses. It’s crucial to highlight that this genetic change does not appear to be widespread among H5 viruses, nor is it anticipated to significantly enhance the ability of influenza viruses to replicate or spread.
Despite the identification of NA-S247N potentially reducing antiviral susceptibility in laboratory settings, this change has not been classified as resistance. Laboratory results showing reduced inhibition by oseltamivir do not necessarily reflect diminished effectiveness when treating patients infected with H5N1. The CDC continues to endorse oseltamivir as the antiviral treatment of choice for H5N1 patients, including post-exposure prophylaxis for close contacts of confirmed cases and individuals with higher risk exposures to infected animals.
Due to the observed low viral RNA concentrations in clinical specimens from these specific cases and challenges in virus isolation attempts, several sequencing efforts were required to yield adequate data for posting partial NA sequences. Furthermore, CDC identified a different change in the polymerase acidic (PA) protein in a confirmed human case of H5N1 bird flu in California (A/California/150/2024). This alteration, denoted as PA-I38M, is associated with reduced susceptibility to the antiviral medication baloxavir marboxil, although it has only been sporadically identified in a limited number of avian influenza viruses. Notably, baloxavir is not recommended for H5N1 treatment or post-exposure prophylaxis. As mentioned, oseltamivir remains the recommended antiviral for H5N1 bird flu cases. Notably, no patients in the U.S. have received baloxavir treatment for H5N1. There exists a lack of data regarding the treatment of H5N1 patients with baloxavir worldwide, rendering the optimal dosing and duration for human use undefined.
The genetic sequencing data from these and other recently confirmed human cases of H5 bird flu have been made accessible on public platforms such as GISAID and GenBank. Additional laboratory investigations are ongoing and planned within the CDC to further discern the implications of these genetic alterations amidst the ongoing spread of H5 viruses. In summary, while the specific changes noted have not proliferated widely and are not spreading among infected poultry or cattle, these developments underscore the critical need for continuous surveillance and testing in monitoring H5 viruses for any potential changes affecting antiviral susceptibility.
<h2>Surveillance Update</h2>
As previously highlighted, the CDC has confirmed 11 cases of H5 bird flu in Washington state in addition to 26 confirmed cases in California. The CDC remains committed to supporting state health departments in monitoring individuals who have been exposed to infected cows, birds, or other domestic or wild animals that may carry the avian influenza A(H5N1) virus. To date, over 7,300 individuals have been under observation due to such exposures, with at least 380 people developing flu-like symptoms, including conjunctivitis, participating in this targeted testing initiative. More comprehensive information regarding ongoing monitoring efforts is readily available at CDC's Symptom Monitoring Among Persons Exposed to HPAI webpage.
Moreover, since February 25, 2024, public health laboratories have conducted tests on more than 60,000 specimens for the avian influenza A(H5) virus along with other novel influenza strains. Among these, one specimen collected during routine surveillance was identified as presumptively positive for the avian influenza A(H5) virus and subsequently confirmed as H5N1 by CDC.
The CDC continuously reviews influenza surveillance data through its 2024-2025 influenza surveillance strategy, particularly in regions where avian influenza A(H5N1) has been detected among dairy cattle or other animal populations. This monitoring aims to identify any unusual trends in flu-like illnesses, conjunctivitis, or activity pertaining to influenza viruses. According to the latest weekly surveillance data, the CDC’s flu surveillance systems have not reported indicators of any unusual flu activity among the overall population.
<h2>Outreach Update</h2>
On Tuesday, November 12, and Wednesday, November 13, the CDC facilitated a bilingual radio media tour aimed at journalists covering the flu. This initiative enabled participants to engage with CDC experts discussing the ongoing Seasonal Flu Vaccine Program for Livestock, Dairy, and Poultry Workers currently being implemented in 12 states. Through these dialogues, the emphasis was placed on the vital role of seasonal flu vaccination in mitigating seasonal flu risks among agricultural workers.
In line with its outreach efforts, the CDC has launched a new "Toolbox Talk" specifically addressing personal protective equipment for H5 bird flu. Toolbox Talks serve as structured guides designed for focused discussions with workers regarding potential hazards they might face in their occupational settings. This particular guide aims to equip employers with the tools to discuss proper usage of PPE to prevent exposures related to H5N1, incorporating brief presentations detailing how PPE functions, guidelines for safely donning and doffing PPE, and essential information for maintaining safety while utilizing such equipment.
The CDC continues to bolster outreach initiatives directed at farm workers regarding H5N1 bird flu. This outreach includes targeted messages aimed at farm workers in affected counties through Meta platforms (Facebook and Instagram), alongside digital display ads and audio content on platforms such as Pandora. Furthermore, CDC is actively broadcasting advertisements on local radio stations approximately 30 times weekly to connect with individuals who may not utilize social media platforms. These outreach efforts aim to disseminate vital information in both English and Spanish concerning the risks associated with H5N1 bird flu infection, recommended preventive measures, relevant symptoms to monitor, and actions to take in the event of symptom development. Metrics regarding outreach efforts are summarized in the accompanying Table 1. Additionally, the CDC is formulating a broader outreach strategy to raise awareness about the availability of free seasonal flu vaccinations for farm workers in states directly impacted by H5N1 this season.This version enhances details while ensuring the essence of the original information remains intact.
What specific resources are available for employers of farm workers regarding avian influenza and seasonal flu vaccinations?
**Interview with Dr. Jane Thompson, CDC Infectious Disease Specialist**
**Editor:** Thank you for joining us today, Dr. Thompson. With the recent CDC initiative aimed at supporting farm workers regarding avian influenza and seasonal flu vaccinations, can you tell us more about the resources being provided to employers of farm workers?
**Dr. Thompson:** Absolutely! The CDC has introduced a comprehensive suite of resources for employers in the agricultural sector, focusing on health safety and vaccination protocols. This includes guidelines on identifying symptoms, requirements for protective measures, and protocols for vaccination to mitigate risks associated with avian influenza, particularly the H5N1 strain.
**Editor:** In your recent updates, you mentioned a troubling multistate outbreak of avian influenza. Can you elaborate on the impact this has had, particularly with farm workers?
**Dr. Thompson:** Yes, indeed. We have seen a significant increase in cases, especially among farm workers in states like California and Oregon. So far, 52 confirmed cases have been reported, and notably, 26 have been linked to dairy farm workers in California. The symptoms have generally been mild and primarily include conjunctivitis, with no hospitalizations required thus far.
**Editor:** That’s reassuring to hear. What actions is the CDC taking in response to the situation, given the multi-agency collaboration?
**Dr. Thompson:** The CDC is collaborating closely with the USDA, FDA, and ASPR, utilizing a One Health approach that considers human, animal, and environmental health. We’re continuously monitoring the situation, conducting epidemiological investigations, and ensuring that health officials are well-informed about potential exposures and risks.
**Editor:** In regard to the genetic sequencing of viruses, how concerning are the recent changes, such as the identified genetic alteration NA-S247N?
**Dr. Thompson:** While the NA-S247N change suggests a possible reduction in susceptibility to the antiviral medication oseltamivir, it’s important to note that this has not been classified as resistance. The data indicates that although there are slight variations, the overall effectiveness of oseltamivir as a treatment remains intact, and the CDC continues to endorse it for H5N1 cases.
**Editor:** You also mentioned monitoring efforts targeting individuals with exposure to infected animals. Can you provide some insight into how that process works?
**Dr. Thompson:** Certainly! We have been vigilant in observing over 7,300 individuals who have had direct exposure to infected animals. This includes monitoring for symptoms like conjunctivitis or flu-like symptoms. It’s a critical part of our surveillance strategy to quickly identify and manage potential cases and prevent further spread.
**Editor:** Lastly, how is the CDC addressing outreach to agricultural workers regarding vaccination against seasonal flu?
**Dr. Thompson:** The CDC recently held a bilingual radio media tour to discuss our Seasonal Flu Vaccine Program for livestock, dairy, and poultry workers. We’re really focusing on educating these workers about the importance of vaccination in protecting not just their health, but also the broader agricultural community.
**Editor:** Thank you, Dr. Thompson, for your insights. It’s great to see the proactive steps being taken to safeguard public health, especially within vulnerable worker populations.
**Dr. Thompson:** Thank you for having me! It’s a team effort, and we appreciate the opportunity to share this vital information with the public.
