Costco Wholesale, the fifth largest general retailer in the United States, is sending letters to nearly 300,000 customers in the country’s northwest and midwest regions, informing them that they might have bought meat that is subject to recall because of possible E. coli bacteria contamination, U.S. media reported on Tuesday.

On June 28, JBS Swift Beef Company in the U.S. state of Colorado announced that it will recall additional 380,000 pounds of assorted beef primal products that may be contaminated with E. coli O157:H7 bacteria.

About 4,300 pounds of the recalled meat were supplied to Costco and made into fresh steaks, ribs and ground beef products, The Seattle Times said in a report.

According to the newspaper, Costco on Tuesday called about 267,000 customers who bought products made from the recalled meat and is sending letters to about 297,000 customers who overlap with the people who were called, asking them to return the products for a refund.

Headquartered in Issaquah in the U.S. state of Washington, Costco is billed as the largest membership warehouse club chain in the world based on sales volume. It now operates over 400 warehouses in the United States.

On June 24, JBS already started a voluntary recall of 41,280 pounds of whole muscle cut beef products that may have been contaminated with E. coli bacteria.

The recall was then expanded after an investigation of 24 illnesses by the U.S. Department of Agriculture (USDA) and the Centers for Disease Control and Prevention found that at least 18 of the illnesses appeared to be associated with the contaminated meat, prompting JBS to re-examine the effectiveness of its food safety system.

The beef products subject to the latest recall ‘were distributed both nationally and internationally,’ the USDA said earlier in a statement.

E. coli O157:H7 is a potentially deadly bacterium that can cause bloody diarrhea, dehydration, and in the most severe cases, kidney failure, the USDA said, noting that the very young, seniors and persons with weak immune systems are the most susceptible to the food borne illness.