Wisconsin
US Midwest state; site of the first US dairy H5N1 detection.
Last refreshed: 7 May 2026
What made Wisconsin the first state to detect H5N1 in dairy cattle, and is Idaho repeating the pattern?
Timeline for Wisconsin
Mentioned in: Idaho dairy H5N1 breaks five-month US lull
Pandemics and Biosecurity- When was H5N1 first found in Wisconsin dairy cows?
- Wisconsin dairy cattle tested positive for H5N1 in December 2025, making them among the earliest confirmed detections in US dairy herds. These were the last known US dairy cases before Idaho's May 2026 detections.Source: CIDRAP
- Why is Wisconsin important in the H5N1 dairy cattle story?
- Wisconsin's December 2025 H5N1 dairy detections were the baseline for US dairy surveillance before a five-month apparent gap ended with Idaho's May 2026 confirmations. Wisconsin's concentration of dairy farms makes it a key state in tracking bovine H5N1 spread.Source: CIDRAP
Background
Wisconsin is a state in the Upper Midwest of the United States, bordering Lake Michigan and Lake Superior to the east and north respectively. Its capital is Madison; Milwaukee is the state's largest city. Wisconsin has a population of approximately 5.9 million. The state is one of the leading dairy-producing states in the country, commonly marketed under the slogan 'America's Dairyland,' with a dense concentration of dairy farms and cheese-processing operations. Agriculture, manufacturing, and higher education anchor its economy. The University of Wisconsin-Madison is a leading research institution. Wisconsin's dairy industry relies on a large farm workforce, making occupational exposure to livestock pathogens a standing public health consideration.
Wisconsin dairy cattle were among the first in the United States to test positive for H5N1, with confirmed detections in December 2025 . These detections were the background against which the five-month gap before Idaho's May 2026 confirmations was judged: that gap had read as quietly reassuring until Idaho broke it. Wisconsin's December 2025 cases are cited in the briefing as the baseline reference point for the most recent prior US dairy H5N1 activity, making the state a named node in the ongoing US dairy H5N1 timeline.
