(NewsNation) — Six workers were found to have contracted avian flu, or bird flu, from a single farm in Colorado, the biggest outbreak of the disease in the U.S. so far.

This is the first time multiple cases of bird flu have been connected to one incident. The workers were all involved in culling poultry that had contracted the illness, a standard practice when bird flu is discovered in a flock.

High temperatures are believed to have contributed to the outbreak, as temperatures around 100 degrees made it difficult for workers to wear personal protective equipment (PPE). While PPE is recommended by the Department of Agriculture to help slow the spread of H5N1, there is no requirement that workers use it.

The workers experienced mild respiratory and eye symptoms and the strain of the virus was found to be similar to that found in Michigan.

The good news is that there is no evidence of human-to-human transmission and the similarities to Michigan indicate the virus has not evolved significantly.

However, there are still concerns that a bird flu epidemic could develop in the U.S. as states have taken varying approaches to testing and protecting cattle or workers, making it difficult to tell how widespread bird flu is in cows or people.

While traces of bird flu have been found in milk, authorities say pasteurization is sufficient to kill the virus and there is little to no risk in consuming pasteurized milk or beef cooked to Department of Agriculture recommendations.