The US Food and Drug Administration warned people on Thursday about the possibility to find tainted infant formula from China on sale at ethnic groceries nationwide and urged them to avoid buying it.

The warning comes after 59 infants in China from a rural area of northwest Gansu province have been diagnosed with kidney stones this year after being fed with low-price powdered milk. One of the infants died. Similar cases also occurred in Jiangsu, Ningxia, Gansu, Shandong, Anhui and Hunan. There were no cases of kidney stones in 2006 and 2007.

On a thorough analysis, the formula sold in China was found to be contaminated with melamine, a chemical used in making plastics. The same substance was found in pet food ingredients from China and linked to the deaths and illnesses of hundreds of cats and dogs in 2007. Melamine can make food appear to have higher levels of protein in testing but can also cause kidney failure.

All the babies had all been fed the same brand of low-price powder milk sold under the “Sanlu” brand, manufactured by a leading Chinese dairy products company, the report revealed.

However, the Sanlu Group has stated that the powder milk involved in the scandal was counterfeit. In addition, it has dispatched teams to independently investigate the Gansu incident.

It is not the first time China confronts with a milk-related problem. Four years ago, 13 infants died of nutritional deficiencies after being fed substandard milk powder. About 170 other babies suffered from malnutrition and other symptoms including swollen heads and an inability to grow after being fed deficient milk powders. The case triggered widespread investigations into food and health safety at the time. Lab analysis revealed that the formula involved in the scandal was made of starch, flour and sugar.

Although no Chinese brands of powdered milk are approved for export to the United States, the US regulators are concerned that some Chinese formula may be on sale at ethnic groceries particularly in places like New York and San Francisco that have large populations of Chinese immigrants.

“We have some concerns that there may be some supplies of infant formula that may have gotten into the country illegally and may be in specialty markets that serve the Chinese community,” Janice Oliver, deputy director of the FDA’s Center for Food Safety and Applied Nutrition, said in an interview.

At the same time, she wanted to assure people that “there is no threat of contamination in the domestic supply of infant formula.” Also, none of the manufacturers of baby formula in the United States receive ingredients from China.

The US makers of milk-based baby formula currently approved by the Food and Drug Administration are Abbott Nutrition, Bristol-Myers Squibb unit Mead Johnson Nutritionals, Nestle USA, PBM Nutritionals and Solus Products.