The recent H5N1 bird flu outbreak has raised global concern as cases spread rapidly across both wild and domestic bird populations, with notable spillover events affecting mammals and posing potential risks to humans.
H5N1, a highly pathogenic strain of avian influenza, has historically led to severe economic impacts within the poultry industry and presents serious public health concerns due to its ability to infect multiple species.
The Centers for Disease Control and Prevention (CDC), health officials, and scientists are closely monitoring the situation to understand transmission patterns, assess risks to human health, and coordinate response strategies aimed at containing the virus.
H5N1 Bird Flu Outbreak Update: New Cases in Washington and California
In the ongoing H5N1 bird flu outbreak in the United States, the CDC has reported nine new human cases this week, including six in Washington state and three in California. This brings the total number of confirmed human cases in the United States to 36, an expansion of the outbreak that has affected both dairy and poultry operations across the country.
Current Situation Overview
The outbreak, which began affecting U.S. dairy cows and poultry in March 2024, has now spread to 387 dairy herds across 14 states. California continues to be the epicenter of new infections among cattle. The poultry sector has also been severely impacted, with USDA reporting H5 detections in 67 flocks (39 commercial and 28 backyard), affecting over 22 million birds.
Of the 36 confirmed human cases, 15 were linked to infected poultry exposure, while 20 were connected to sick dairy cows. One case in Missouri, reported in September, has an undetermined source of exposure. California leads with 16 confirmed cases, including three new ones from last week. The six cases in Washington state represent the first human infections in that region.
Human Cases Analysis
The CDC said that all cases so far appear to be isolated instances of animal-to-human transmission, with no evidence of person-to-person spread. Most infected individuals have experienced mild symptoms, primarily:
- Eye redness and discharge (conjunctivitis)
- Mild upper respiratory symptoms (particularly in Washington cases)
None of the cases required hospitalization.
Laboratory Findings
Detailed genetic analysis of the California cases has revealed important information about the virus:
- All sequenced cases show H5N1 viruses from clade 2.3.4.4b
- The viruses are closely related to those infecting dairy cattle
- Full genome sequencing of four California cases confirms B3.13 genotype viruses
- No mutations indicating increased human transmission risk or antiviral resistance
- No signs of additional mammalian adaptation
The CDC has successfully isolated the virus from nine of the 16 California cases and continues testing additional specimens. Researchers are conducting antigenic characterization and antiviral susceptibility testing to ensure existing vaccine candidates remain effective against current strains.
Surveillance and Monitoring Efforts
The CDC has implemented comprehensive surveillance measures:
- Over 6,100 people with potential exposure to infected animals have been monitored
- More than 300 individuals with flu-like symptoms have undergone specific testing
- Public health labs have tested over 55,000 specimens for avian influenza A(H5) since February 2024
- Regular monitoring of flu surveillance data, particularly in affected regions, shows no unusual trends in human flu activity
Field Response
The CDC has deployed multilingual field teams to both California and Washington to support local health authorities:
- In California:
- Teams are investigating the outbreak’s origins
- Working to reduce risk to farm workers
- Conducting active surveillance
- Managing field assessments of suspected cases
- Coordinating testing and treatment
- Distributing information to workers and communities
- In Washington:
- Supporting monitoring during infected poultry farm depopulation
- Conducting on-site symptom screening
- Testing workers at shift changes
- Providing antiviral medication (oseltamivir)
- Assisting with data management and epidemiological investigations
Public Health Response and Outreach
The CDC has launched a comprehensive outreach campaign targeting farm workers in affected areas:
- Multilingual information distribution through social media platforms (Meta, Facebook, Instagram)
- Digital display and audio messaging via Pandora
- Local radio station advertisements running approximately 30 times weekly
- Materials available in both English and Spanish
The information campaign focuses on:
- Potential infection risks
- Recommended preventive measures
- Symptom awareness
- Response protocols for those developing symptoms
- Access to free seasonal flu vaccinations for farm workers in affected states
Risk Assessment
Despite the increase in cases, the CDC maintains that the immediate risk to the general public remains low. However, individuals with direct exposure to infected animals face an elevated risk of infection. The agency continues to emphasize the importance of proper protective measures for those working with potentially infected animals.
Ongoing Investigations
Teams are currently:
- Processing additional test specimens from Washington state
- Continuing virus isolation and sequencing efforts
- Monitoring for any signs of viral mutations or adaptation
- Investigating potential new cases in affected regions
- Evaluating the effectiveness of current prevention strategies
The CDC continues to work closely with various partners, including:
- U.S. Department of Agriculture (USDA)
- Food and Drug Administration (FDA)
- Administration for Strategic Preparedness and Response (ASPR)
- State public health departments
- Animal health officials
Recommendations
The CDC has issued important safety guidelines to protect against H5N1 bird flu infection:
- Avoid contact with sick or dead animals, including wild birds, poultry, and dairy cows. This extends to avoiding animal waste, bedding materials, and any items that may have been contaminated by infected animals.
- The agency specifically warns against consuming unpasteurized (raw) milk, as it could transmit the virus. Pasteurized milk remains safe to drink since the process effectively kills the H5N1 virus.
- For workers who must handle potentially infected animals, proper protective measures are crucial. The CDC emphasizes the importance of wearing recommended personal protective equipment (PPE) during any interaction with suspected or confirmed infected animals.
These guidelines are part of the CDC’s comprehensive approach to preventing H5N1 infections in humans. The agency continues to monitor the situation and conduct public health investigations to better understand and control the spread of the virus. Workers in high-risk settings should familiarize themselves with these safety protocols and follow them strictly to minimize exposure risk.
Food Poisoning News has previously provided extensive coverage of this ongoing public health challenge, including:
- FDA affirms safety of milk despite bird flu traces in dairy cattle
- Bird flu outbreak confirmed in three California dairy herds
- New research sheds light on spread of H5N1 flu in dairy cattle
Commenting on this story, one national food poisoning lawyer said, “I strongly second the recommendation by the CDC that consumers should avoid drinking raw milk. Not only can bird flu be transmitted through untreated milk, but also the raw milk can carry E. coli, salmonella, or campylobacter, all dangerous pathogens that can cause severe, and sometimes, life-threatening illness.”
Food Poisoning News has also covered several outbreaks this year linked to the consumption of raw milk including an outbreak of salmonella tied to raw milk that sickened 165 people in California and a recent recall of raw milk in Connecticut due to potential campylobacter contamination.
