Monitoring Workers Exposed to H5N1 Avian Influenza in Michigan, 2024

On March 25, 2024, highly pathogenic avian influenza (HPAI) A(H5N1) virus was detected in cows on a Texas dairy farm. The virus had already been found in U.S. wild birds and mammals, poultry and dairy facilities, and a Texas dairy worker had been reported infected in April 2024. After cows were moved between states, the outbreak spread widely: from March 25 to June 17, animals on 102 dairy farms in 12 states, 24 commercial poultry flocks in five states and many backyard flocks tested positive. This report from Michigan's Department of Health and Human Services describes how monitoring exposed workers found the second and third human cases of the 2024 outbreak.

The virus in Michigan

Infected cows from Texas brought the virus to a Michigan dairy, where it was detected on March 29. By late May, 23 dairies in 10 counties and seven commercial poultry facilities in four counties were affected — as of May 23, the most affected dairy and poultry facilities of any state in the outbreak. The virus was also found in a backyard flock and in pigeons, foxes, cats, opossums and a raccoon. Whole-genome sequencing suggested every isolate sequenced since March 2024 traced back to Texas.

Monitoring exposed people

Public health officials tracked people exposed to infected animals and tested anyone who developed symptoms.

• Dairy workers: 306 people at the 23 affected dairies had been exposed. Officials got worker lists from 20 of the farms; workers at 12 were enrolled in daily text-message symptom checks, and those at the other eight were monitored through a farm contact. Some were followed for more than 50 days because it was unclear when their exposure ended. Twenty (6.5%) reported symptoms and were tested.
• Poultry workers: 857 people at the seven affected poultry facilities had been exposed, and lists came from every facility. Eighteen (2.1%) developed symptoms and were tested; all were negative.
• Others: 125 people, including federal and state responders and people exposed to infected domestic or wild animals, were monitored. Fifteen reported symptoms, and 14 of them tested negative.

In all, 1,288 Michigan residents were monitored, 53 (4.1%) reported symptoms and 52 were tested.

Two cases

Two dairy workers, from different farms, tested positive — 3.8% of those tested and fewer than 1% of monitored dairy workers.

• The first developed mild conjunctivitis in one eye after raw milk from an infected cow splashed into it; the virus was found in an eye swab, much like the Texas case.
• The second developed respiratory symptoms after close contact with sick cows and tested positive on a nasal swab.

Both illnesses were mild, neither worker was hospitalized, and no household or work contacts fell ill. Both had worn some protective equipment, but neither had worn a mask or respirator.

Lessons

The risk to the public remained low, but novel influenza A viruses such as H5N1 have pandemic potential. The authors stress notifying people exposed to infected animals, educating them and giving them access to protective equipment — including eye and respiratory protection — monitoring for symptoms, testing anyone who becomes ill, and offering antivirals quickly. The mild cases might have gone unnoticed without cooperation among state officials, farms and workers, and simple, unobtrusive monitoring such as text messages may encourage people to take part. A One Health approach, working with agriculture departments, farms and workers, is essential.

Sources

• Joseph Coyle, Natasha Bagdasarian, Seth Eckel and colleagues, Michigan Department of Health and Human Services, "Notes from the Field: Health Monitoring, Testing, and Case Identification Among Persons Exposed to Influenza A(H5N1) — Michigan, 2024," Morbidity and Mortality Weekly Report, CDC: https://www.cdc.gov/mmwr/volumes/73/wr/mm7329a4.htm
• The source spells raccoon "racoon."