The recent detection of highly pathogenic avian influenza, commonly known as bird flu, has been confirmed in three additional dairy herds in Michigan counties: Ionia, Isabella, and Ottawa, the Michigan Department of Agriculture and Rural Development said Friday. That brought the total to four affected counties, with Montcalm County the first to detect the disease in a dairy herd about two weeks earlier.

Tim Boring, director of the Department of Agriculture and Rural Development, said Michigan’s situation mirrors the outbreaks occurring in various states across the country.

Federal and state health authorities said the commercial milk supply remains safe for consumers due to stringent animal health requirements and the pasteurization process. Pasteurization involves heating liquids to high temperatures for a short period to destroy bacteria and viruses, such as influenza. In Michigan, all milk sold in stores must be pasteurized according to state law.