To get to grips with the outbreak, the US Department of Agriculture, USDA, has now ordered tests of unpasteurized milk across the country.
Farms, tank trucks, and dairies will be tested to track new outbreaks and get an overview of the spread in order to combat it.
Milk farmers and dairy companies have opposed the testing, fearing that sales will decline, but the USDA emphasizes in a press release that people run a very small risk of being infected through milk products.
Pasteurization of milk kills the virus and makes the drink safe to consume. The USDA, on the other hand, warns against drinking unpasteurized milk.
The authorities ordered mandatory tests for milk cows crossing state borders in April, but it has not stopped the spread.
This year, at least 58 people in the US have been infected with bird flu, most of them working near cows.
