Fragments of bird flu were found in 20% of retail milk samples taken in the US by federal regulators.

Initial results from the nationally representative study by the Food and Drug Administration (FDA) show fragments of highly pathogenic avian influenza (HPAI) in one in five retail samples.

In an online update, the FDA said there is a higher proportion of positive results coming from milk in areas with infected herds.

Several samples of retail powdered infant formula were tested, as well as powdered milk products marketed as toddler formula.

“All qPCR results of formula testing were negative, indicating no detection of viral fragments or virus in powdered formula products,” a statement from the FDA said.

No risk to human health

There is no evidence that the disease poses a risk to human health or that the live virus is present on shop shelves, the FDA added.

The FDA and the US Department of Agriculture (USDA) have indicated that based on the information currently available, US commercial milk supply is safe because of the pasteurisation process and the diversion or destruction of milk from sick cows.

The USDA previously confirmed HPAI had been found in a number of dairy herds in the US.

The illness causes decreased lactation, low appetite and other symptoms in dairy cows.

The authorities in the US said the disease appears to have been introduced by wild birds.

HPAI is a disease that is highly contagious and often deadly in poultry, caused by highly pathogenic avian influenza A (H5) and A (H7).