Colorado health authorities reported four confirmed cases of H5N1 bird flu virus in poultry workers, with a fifth case currently under investigation, announced on Sunday.

Human infections with the H5N1 avian influenza can lead to severe disease and potentially trigger a pandemic if the virus mutates to transmit more readily between individuals, according to the U.S. Centers for Disease Control and Prevention (CDC).

The state's public health department confirmed that the CDC has verified four cases, with a fifth case awaiting confirmation. The agency is assisting with further investigations.

"A fifth worker's samples tested presumptively positive at the state laboratory on Saturday and are being forwarded to the CDC for confirmation," the department stated.

The affected workers exhibited mild symptoms, ranging from conjunctivitis to respiratory issues; however, none required hospitalization.