Drugmaker Abbott Laboratories said Wednesday it is recalling millions of containers of its best-selling Similac infant formula that may be contaminated with insect parts.

The voluntary action affects up to 5 million Similac-brand powder formulas sold in the U.S., Puerto Rico, Guam and some Caribbean countries. The company said the products may contain a small beetle or larvae, which could cause stomach ache and digestion problems.

The recall does not affect any liquid formulas or other Abbott-brand products.

A company spokeswoman said Abbott uncovered the insects last week in one section of a manufacturing plant in Sturgis, Michigan.

“We immediately shut down that one area and began an investigation,” said Abbott’s Melissa Brotz. “We’re in the process of resolving it now.” Abbott manufactures Similac at several U.S. sites.

Brotz said the company has been consulting with the Food and Drug Administration, which determined there was no “immediate health risk” from the contamination.

Consumers can enter the lot number on their containers online to determine if they are subject to the recall. The products should be returned to Abbott for a full refund.

“Delivering anything less than the highest quality infant formula is unacceptable to us,” said Brotz. “We will do whatever is necessary to maintain the trust of parents in the coming weeks.”

The affected products were sold in plastic containers and various can sizes, including 8-ounce (227-gram), 12.4-ounce (352-gram) and 12.9-ounce (366-gram).

Similac is the best-selling infant formula in the U.S. Abbott’s nutritional products — which include adult brands like Ensure — had sales of $5.3 billion last year.

Abbott expects to lose $100 million in connection with the recall. However, the North Chicago, Illinois, company confirmed its third-quarter earnings guidance between $1.03 and $1.05 per share.

Shares of Abbott Laboratories fell 16 cents to $51.99.