Also, a spokesman for one major manufacturer criticized the FDA for its release of the inaccurate information.
"We're getting inundated by calls from moms confused about the situation," said Pete Paradossi, a spokesman for Mead Johnson, one of the three major manufacturers of U.S.-made formula involved in the problem detections.
Melamine is the industrial chemical found in Chinese infant formula - in far larger concentrations
- that has been blamed for killing at least three babies and making at least 50,000 others ill.
The FDA and other experts said the melamine contamination in U.S.-made formula had occurred during the manufacturing process, rather than intentionally as was done in Chinese production. The manufacturers insist their products are safe.
"The levels that we are detecting are extremely low," said Dr. Stephen Sundlof, director of the FDA's Center for Food Safety and Applied Nutrition. "They should not be changing the diet. If they've been feeding a particular product, they should continue to feed that product. That's in the best interest of the baby."
Part of the confusion Wednesday stemmed from the FDA's own statements.
While proclaiming that the very low concentrations detected of melamine and a similar compound called cyanuric acid pose no health danger to infants, the FDA has maintained it is unable to identify any exposure level of melamine in infant formula "that does not raise public health concerns."
Further complicating the situation was inaccurate data that FDA released to The Associated Press, which was first to disclose the formulas' brand names and other details in an investigative report Tuesday.
A spreadsheet the AP obtained from the FDA under a Freedom of Information Act request stated that Mead Johnson's Infant Formula Powder, Enfamil LIPIL with Iron contained traces of melamine.
On Wednesday, FDA spokeswoman Judy Leon said that spreadsheet contained an error
- that the FDA had incorrectly switched the names of the Mead Johnson product with Nestle's Good Start Supreme Infant Formula with Iron. That meant, Leon said, that the Nestle's Good Start had melamine while Mead Johnson's Enfamil had traces of cyanuric acid.
The FDA said last month that the toxicity of cyanuric acid is under study, but that in the meantime it is "prudent" to assume that its potency is equal to that of melamine.
Problems with melamine-spiked formula surfaced this fall in China, where unscrupulous manufacturers intentionally dumped it into watered-down milk to falsely elevate protein levels. The concentrations in China were as much as 2,500 parts per million
- about 10,000 times greater than what the FDA found in the U.S.
The FDA said there have been no reports in the United States of human illness from melamine. The chemical, which legally can be used in product packaging and a solution to clean manufacturing equipment, can bind with other chemicals in urine, potentially causing damaging stones in the kidney or bladder and, in extreme cases, kidney failure.
Mead Johnson spokesman Paradossi said he was frustrated that the FDA had provided inaccurate information for worldwide distribution by the AP. He said the FDA informed his company of the test results, as well as the inaccurate disclosures only Wednesday, during an emergency conference call the agency staged with major manufacturers and the industry's trade group. During a similar call Monday, the FDA told the industry about the upcoming AP investigative report.
Nestle did not returns calls seeking comment Wednesday.