The Centers for Disease Control and Prevention (CDC) has recently raised concerns that some cases of H5N1 bird flu infection in U.S. farmworkers may be going undetected. Despite ongoing outbreaks of bird flu in dairy cattle, limited testing of farmworkers has made it challenging to fully track the virus’s spread among people working in close contact with infected animals. This issue has been further compounded by a lack of health insurance, paid sick leave, and resistance from some farm owners toward increased health monitoring on their properties.
New blood testing conducted by the CDC has shed light on the situation. Results published on Thursday indicate a small but notable number of H5N1 infections that have gone unrecorded among farmworkers in Michigan and Colorado. Blood tests from 115 farmworkers conducted over the summer found evidence of recent infection in eight individuals, with half of them recalling feeling ill around the same time as the cattle were infected. However, the other four reported no symptoms.
Antibody Testing and H5N1 Bird Flu Infection Exposure
The study involved serological testing, which detects antibodies produced in response to the virus. Antibodies remain in the blood long after infection, allowing researchers to identify past exposure and gauge how widely the virus has spread. The findings suggest that while current health efforts are missing some cases, there is no indication that the particular strain of H5N1 bird flu infection tied to this dairy cattle outbreak is spreading from person to person.
Nirav Shah, the CDC’s principal deputy director, stated that the new data had not raised concerns about person-to-person transmission. The CDC continues to consider the risk to the general public as low, despite confirming 45 human cases this year associated with cattle or poultry exposure. The study’s results, however, highlight the need for heightened monitoring of farmworkers and veterinarians who may be at increased risk.
CDC’s Response and New Recommendations
In light of these findings, the CDC has updated its recommendations. Previously, testing was advised only for farmworkers exposed to infected animals who exhibited symptoms. Now, the CDC is calling for all workers exposed to infected animals to be tested for H5N1, regardless of symptoms. This expansion is intended to help identify, treat, and isolate cases early on, including those with mild or undetectable infections. The CDC is also recommending that Tamiflu, an antiviral medication, be provided to high-risk individuals exposed to the virus, particularly those who may have been exposed without adequate protective gear.
The study found that all eight workers with H5N1 antibodies had performed tasks such as cleaning milking parlors, and most had milked cows without respiratory protection. Fewer than half had worn eye protection. Research has shown that H5N1 appears to heavily affect mammary glands; the virus is highly present in the udders of infected cows and can survive on surfaces and equipment for hours, suggesting a significant risk of spread in milking parlors.
Ongoing Challenges and Public Health Risks
Despite the generally mild nature of human cases so far, public health officials remain concerned about the risk of the virus acquiring mutations that could make it more dangerous. Shah emphasized that limiting opportunities for the virus to spread among humans is critical to preventing these mutations. Quick identification, treatment, and isolation of cases are key measures to achieving this.
However, implementing these recommendations presents challenges. The CDC has no legal authority to enforce compliance, and some farmers have been reluctant to allow public health officials access for testing or to provide workers with personal protective equipment (PPE). In some areas, environmental factors further complicate PPE use. For instance, heat waves in California this summer made wearing masks and goggles impractical for farmworkers, increasing the risk of exposure.
Tamiflu, while effective at reducing the viral load and transmission risk, works best when administered within 48 hours of symptom onset. For many farmworkers, who may live in remote areas with limited access to transportation and healthcare, meeting this timeframe can be challenging.
Efforts to Expand Surveillance and Understanding of H5N1 Bird Flu Infection Spread
While the CDC’s study has yielded critical insights, it remains unclear how effective these new recommendations will be in slowing the spread of H5N1 among farmworkers, especially given the realities on the ground. In states like Michigan and Colorado, the CDC has been able to collaborate effectively with farmers to conduct such studies. However, in states like California, where nearly half of the country’s human H5N1 cases have emerged recently, similar efforts have yet to be organized.
The CDC continues to explore ways to understand the spread of H5N1 in farmworkers, veterinarians, and others at risk. In September, around 150 veterinarians at a conference of the American Association of Bovine Practitioners in Ohio provided blood samples for antibody testing, with results expected to offer additional insight into the virus’s reach. The CDC hopes that expanded monitoring and timely treatment will help mitigate potential public health risks associated with undetected H5N1 bird flu infections.
