Craig Langman (who has made a previous appearance on PBFluids) wrote an editorial for the Melamine article and pair of letters to The Journal (one from Wang et al. from Taiwan and the other from Ho et al. from Hong Kong).
He recommends the same advice I have been giving for Americans who have adopted Chinese infants:
How should physicians in other parts of the world care for Chinese infants who may have been exposed to melamine-contaminated powdered infant formula? The American Society of Pediatric Nephrology suggests a conservative approach in asymptomatic infants,PDF since stones presumed to have been induced by melamine ingestion appear to be passed easily after hydration, and there are currently no follow-up reports on the children studied by Guan et al. and Wang et al. Performance of abdominal ultrasonography in all potentially exposed Chinese children living in the United States would be likely to cost many millions of dollars, an expenditure difficult to justify, given that both unaffected and affected children may have no symptoms and that the meaning of a stone in an asymptomatic child is uncertain.
Langman emphasizes that each study is unable to estimate a true incidence because the populations studied were not representative of the population at risk.
He also teases the reader by mentioning that stones, which are increasing in frequency among adults, seem to be increasingly common among children. He states that this may be due to dietary and lifestyle issues but doesn't even entertain the possibility that melamine exposure here in the U.S. and around the world may be responsible. This possibility was first suggested in an insightful article in Slate. We know that melamine is found in the U.S., we don't know how long it has been here.
My personal sense is that the Slate article is just scaring people unnecessarily. if the increase in stones was do to melamine we would know it. We would know it because stones that are removed by interventions are always analyzed in a stone lab. The stones in China that were due to melamine were made of uric acid and melamine. If even a single stone in the U.S. was found to be melamine the whole medical world would go ape.