USDA APHIS issued a Mandatory Testing Order requiring dairy cows to test negative before interstate movement. When Idaho herds tested positive in May 2026, USDA triggered mandatory tracing across the Pacific Northwest dairy supply chain.Source: USDA APHIS

Why has the USDA not updated dairy-worker PPE guidance after the aerosol study?

USDA had not updated its dairy-worker guidance as of publication of the May 2026 Emory PLOS Biology study, which found H5N1 in milking-parlour aerosols. Current guidance was written for contact transmission and does not address the respiratory exposure route.Source: PLOS Biology / Emory University

Where can I find the USDA H5N1 dairy herd detection data?

USDA APHIS publishes its HPAI detection dashboard at aphis.USDA.gov. In 2025, USDA moved animal H5N1 data to a separate tracker from CDC's human case page, creating a gap in publicly available cross-referencing of animal and human detections.Source: USDA APHIS

Background

The United States Department of Agriculture (USDA) is a federal cabinet agency responsible for agricultural policy, food safety, and rural development. Its Animal and Plant Health Inspection Service (APHIS) division is the primary regulator of livestock disease, including the authority to issue mandatory testing orders and movement restrictions for infected herds. USDA operates the HPAI dashboard tracking highly pathogenic avian influenza detections across commercial poultry and dairy, and it co-manages the federal response to H5N1 in dairy cattle alongside CDC and FDA. The agency's budget runs to approximately $200 billion annually, though biosecurity and surveillance programmes represent a fraction of that.

USDA APHIS issued the Mandatory Testing Order for H5N1 in US dairy herds in 2024, requiring all lactating cows to test negative before interstate movement. Idaho dairy herds confirmed H5N1 positive in May 2026, the first US dairy detections since Wisconsin in December 2025, triggering USDA's mandatory tracing requirements across the Pacific Northwest supply chain. USDA also had not updated its dairy-worker guidance to address the aerosol transmission route documented in the Emory PLOS Biology study published the same month, maintaining guidance calibrated for contact transmission rather than submicron particle exposure. USDA moved its animal HPAI data to a separate tracker from CDC's human case dashboard in 2025, creating asynchronous federal data streams that complicate state-level correlation of animal and human detections.

Source Material

United States Department of Agriculture — Wikipedia USDA APHIS HPAI Detection Dashboard

How the World Sees Them

European Union

EU agricultural authorities monitor USDA's H5N1 dairy control measures as a benchmark for whether the US outbreak poses any risk to transatlantic dairy trade.

Japan / South Korea

Major Asian dairy import partners track USDA H5N1 detection data closely and have previously signalled readiness to consider import restrictions if the Idaho outbreak expands geographically.

United States (dairy sector)

Dairy producers view USDA's mandatory testing order as a compliance burden, particularly given the cost of movement restrictions, while public-health advocates argue the order should be expanded to include aerosol-exposure-informed worker protection requirements.