H5N1 bird flu dairy cattle infections in the United States have now crossed a grim new threshold: more than 1,166 dairy herds across 19 states have tested positive since the outbreak began in March 2024, according to USDA data. Yet US health officials continue to classify the risk to the general public as low. This explainer breaks down what the latest USDA and CDC numbers actually show, how much danger farmworkers and the public genuinely face, and what controls are in place on dairy farms to keep the virus from spreading further.
The Outbreak by the Numbers (as of July 2026)
As of July 22, 2026, the US Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) had confirmed more than 1,166 infected dairy herds across 19 states since the outbreak began. Idaho leads the country with a cumulative total of 173 affected livestock premises, almost all of them dairy milking operations. The outbreak traces back to March 25, 2024, when Texas reported the first-ever confirmed H5N1 infection in cows, a species not previously known to carry the virus.
On the human side, the CDC’s qualitative risk assessment counts 70 confirmed human H5N1 cases in the United States since 2024, with 67 of those 70 linked to direct exposure to infected poultry or dairy cows. Three cases had no identified animal exposure. No person-to-person transmission has been detected anywhere in the country. CDC’s FluView surveillance report for week 28, ending July 18, 2026, recorded zero new confirmed human H5 infections that week, and only two H5-positive specimens were identified among more than 67,000 flu-positive specimens tested since late September 2025.
How the Virus Spreads on Dairy Farms
H5N1 has been found in high concentrations in raw, unpasteurized milk from infected cows, and most human infections have followed direct or close contact with sick or dead animals, or with contaminated milk, without the use of recommended personal protective equipment. The virus’s path to cattle followed years of spread through wild birds: highly pathogenic H5N1 has circulated widely in wild aquatic birds worldwide since January 2022, triggering poultry outbreaks in all 50 US states and infections in more than 200 wild terrestrial and marine mammals, before the unprecedented jump into dairy cattle emerged in 2024.
What Human Cases Look Like
The large majority of US human H5N1 infections have been mild, with conjunctivitis, the symptom reported in the first Texas case, among the most common presentations. A smaller number of cases have required hospitalization, and health authorities have reported at least one death associated with the broader outbreak. Virtually every confirmed US case has been traced back to direct occupational exposure, most often among dairy or poultry workers who did not use recommended protective equipment while handling sick animals or contaminated materials.
| Metric | Value (as of July 2026) |
|---|---|
| First confirmed cattle detection | March 25, 2024, Texas |
| Cumulative infected dairy herds | 1,166+ across 19 states |
| State with most affected herds | Idaho (173 cumulative premises) |
| Total confirmed US human cases since 2024 | 70 |
| Human cases with known animal exposure | 67 of 70 |
| Confirmed human-to-human transmission | None identified |
| CDC general public risk level | Low |
| New confirmed human H5 cases, week ending July 18, 2026 | 0 |
Farm and Public Health Controls in Place
USDA APHIS leads the animal-health response, confirming herd detections and coordinating with state agriculture departments, while CDC serves as the lead federal agency for human health. State and local health departments monitor people with known exposure to infected animals for 10 days after contact, and CDC has issued interim recommendations covering personal protective equipment, testing, and treatment for farmworkers and others in contact with potentially infected animals.
On the food-safety side, commercially pasteurized milk and dairy products are considered safe to consume; the pasteurization process inactivates the virus, and the elevated risk is concentrated specifically in raw, unpasteurized milk. CDC also runs multiple surveillance systems, including FluView, the National Wastewater Surveillance System, and the National Syndromic Surveillance Program, to watch for any unusual patterns of flu-like illness that might signal broader human spread.
Limitations and Uncertainties
- Herd-level testing is not uniform nationwide and depends partly on voluntary or triggered testing by state, so the true prevalence of infected herds could be higher than the confirmed count.
- Reported human case totals can lag real-world exposures because of the time needed for symptom onset, testing, and confirmation.
- USDA APHIS testing has not detected genetic changes that would make the virus more transmissible between humans, but health agencies stress that ongoing circulation in mammals continues to create opportunities for the virus to evolve, and this risk cannot be ruled out for the future.
- All figures in this explainer reflect the most recent publicly available USDA and CDC reports at the time of writing (USDA APHIS data as of July 22, 2026; CDC surveillance data through mid-to-late July 2026) and will change as the outbreak continues.
Frequently Asked Questions
Is it safe to drink milk during the H5N1 outbreak?
Yes. Commercially pasteurized milk and dairy products are considered safe, according to the CDC. The primary risk comes from unpasteurized, raw milk, which has been found to contain high concentrations of the virus in infected cows.
How many people have caught H5N1 from dairy cows?
Most of the 70 confirmed US human H5N1 cases reported since 2024 have been linked to direct exposure to infected dairy cows or poultry; 67 of the 70 had a known animal exposure, and no person-to-person spread has been detected.
How many dairy herds have been affected?
As of July 22, 2026, USDA APHIS had confirmed more than 1,166 infected dairy herds across 19 states since the outbreak began in March 2024, with Idaho recording the highest cumulative total at 173 affected premises.
What is the CDC’s official risk assessment for the general public?
The CDC continues to classify the risk to the general public as low. People with job-related or recreational exposure to infected poultry, dairy cattle, or other animals face a higher risk and are advised to use personal protective equipment and report flu-like symptoms promptly.
Could H5N1 become a bigger pandemic threat?
USDA testing to date has not detected genetic changes that would make the virus more transmissible between humans, and no human-to-human spread has occurred in the United States. However, health agencies continue close surveillance because ongoing circulation in cattle and other mammals increases the opportunities for the virus to evolve over time.
Bottom Line
More than two years into the outbreak, H5N1 in US dairy cattle keeps expanding by the numbers — over 1,166 herds and 19 states — but the human side of the picture has stayed remarkably stable: no confirmed person-to-person spread, mostly mild illness among exposed workers, and a public health risk that CDC still rates as low for the general population. The controls that matter most right now are occupational: protective equipment for farmworkers, prompt testing, and avoiding raw milk, rather than any change in everyday behavior for most people.
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