Protective Gear on Colorado Dairy Farms During the 2024 H5N1 Outbreak

This page summarizes a report in CDC's MMWR by the Colorado Department of Public Health and Environment and CDC, on interviews carried out in July and August 2024.

On April 25, 2024, Colorado found highly pathogenic avian influenza A(H5N1) in cows on a dairy farm, and during April–August another 63 dairy farms with infected cows were identified. The risk of the virus passing from animals to people is low, but it has happened in the United States, including to a Colorado dairy worker in 2024 and to poultry workers in 2022 and 2024.

Unlike infected poultry, which usually die quickly in large numbers, infected cows tend to recover (under 2% of a herd dies) and need care, including milking, while ill. Contact with sick cows and with raw milk from acutely infected cows is a risk to workers.

What CDC recommends

For anyone in contact with or near dairy cows, raw milk or items that might be contaminated, CDC recommends personal protective equipment (PPE): fluid-resistant coveralls, a NIOSH-approved particulate respirator such as an N95, goggles, a head or hair cover, gloves, and boots or boot covers, with an optional waterproof apron and face shield.

The Colorado Departments of Public Health and Environment and of Agriculture worked together on the dairy outbreaks. They offered farm owners site visits on protecting workers, sent dairies and industry partners a letter on prevention and PPE, and offered every Colorado farm, before or during an outbreak, a free one-month supply of N95 respirators, surgical masks, face shields, goggles and nitrile gloves.

The survey

• Farms: three affected farms within 50 miles of one another, a convenience sample of about 250 workers, chosen after the state contacted 43 affected farms. One had ordered PPE before the virus was detected; the other two received it at the first public health visit after detection.
• Workers: 83, interviewed anonymously and voluntarily in English or Spanish (72, or 87%, in Spanish), with a gift card for taking part. Nothing was shared with employers. Interviews came a median of 48 days after infected cows were reported.
• Exposure: 44 workers (53%) reported contact with ill cows from the week before the virus was first detected.

Their jobs. The most common duties were milking or working in the milking parlor (51%), cleaning manure (49%) and moving cows (46%); the least common were repair, maintenance and hospital pen work (20%), breeding and artificial insemination (18%), and milk transport (12%). Once the virus was found, the median number of duties per worker fell from five to three.

What they wore

Before the outbreaks, workers reported access to gloves (88%), eye protection (76%), rubber boots or boot covers (71%) and head covers (69%).

Use of gloves, boots, head covers and eye protection was higher in the week after detection than the week before. Workers who moved cows, cleaned manure and milked reported the most use of these items, and their average use rose 28% after detection. The biggest rise was in eye protection while milking, up 40%. Some workers also wore sunglasses, bandanas or gaiters, which are not recommended PPE.

Why it matters

• Milking is the riskiest job. Milking, the most common duty, is thought to carry the highest risk because of raw milk exposure; a Michigan dairy worker with H5N1 had reported milk splashing into the eyes. The rise in eye protection during milking is important. Because cows can be infected without symptoms, PPE is needed while milking every cow on an affected farm, not only visibly sick ones.
• Respirators are hard to wear here. Manure and milk can soil respirators and masks, and the heat and humidity of milking parlors make them uncomfortable, especially in summer. Workers used other masks more than N95s.
• Relationships help. Public health PPE distribution, education and collaboration with the Department of Agriculture may have raised PPE use and lowered risk. Messaging consistent with CDC recommendations, industry engagement to limit worker contact with cattle and milk, and getting PPE onto farms before outbreaks might raise use further, especially during milking. Health agencies should also help owners recognize and report signs of illness in workers.

Limitations

• Some PPE worn before the outbreaks may have been for other reasons, such as gloves for rough materials or head covers against the sun.
• Farms that work with public health may be more likely to request PPE and to take part in studies, and all three received PPE from public health before or right after detection.

Sources

• Marshall KE, Drehoff CC, Alden N, et al. "Personal Protective Equipment Use by Dairy Farmworkers Exposed to Cows Infected with Highly Pathogenic Avian Influenza A(H5N1) Viruses — Colorado, 2024." MMWR 73(44). https://www.cdc.gov/mmwr/volumes/73/wr/mm7344a2.htm
• The report also states that 37 (64%) of "the 58 affected farms" ordered PPE, a count that does not match its other farm totals; that figure is left out here. The report's figure is not reproduced, because the report was prepared jointly with the Colorado Department of Public Health and Environment.