One of the top egg producers in the U.S. confirmed that a farm tested positive for cases of bird flu over the weekend, the company said in a statement Tuesday.

The humble egg, one of nature’s perfect foods, a self-packaged, relatively inexpensive source of protein that can serve as a lowly hangover remedy or help a souffle rise to heavenly heights, is also a great teacher. It’s helping Americans understand how a free-market economy works: When demand is high and supply is low, prices rise.

As egg prices continue to climb, some grocery stores in Massachusetts are limiting how many customers can buy.

The bird flu has been infecting American flocks for years, leading to a series of infections and increased egg prices. But now, there's a new twist: A different strain has been detected in U.S. poultry.