Melamine-tainted milk product-associated urinary stones in children

Background: An outbreak of urinary stones related to consumption of melamine-tainted milk products (MTMP) occurred in China in 2008. The aim of the present study was to evaluate such children to identify their clinical features and risk factors. Methods: Renal ultrasound was performed for 7328 children who presented to a Sichuan teaching hospital between 13 September and 15 October 2008 due to concern of such stones. Clinical data, family information, feeding history and urinary stones were analyzed. Results: Of the 7328 children, 189 (2.58%) had ultrasound findings of urinary stones, and 51 were admitted. Age (mean +/- SD) was 27.4 +/- 25.5 months, and 101 were male and 88, female. The odds ratio (OR) for urinary stones for infants and young children (1-3 years) as compared to older children (>3 years), was 2.42 (95% confidence interval [CI], 1.64-3.56; P < 0.0001) and 1.95 (95% CI, 1.31-2.89; P < 0.0011), respectively. Independent risk factors associated with urinary stones included consumption of MTMP with melamine at >5500 mg/kg (OR, 13.3; 95% CI, 6.8-26.1, P < 0.0001) as compared to that with melamine at <200 mg/kg, and younger father (P = 0.0006). On logistic regression, the only risk factor associated with inpatient care was lower family income per person (OR, 4.4; 95% CI, 1.2-15.9, P = 0.02). Repeat ultrasound for 51 children at mean follow up of 15.3 +/- 8.9 days found that 33 passed out all stones, which was associated with a larger number of smaller stones (P = 0.003). Urinary stones contained melamine and uric acid, but no cyanuric acid. Conclusions: MTMP-associated urinary stones were more frequent in young children and more severe in children from poorer families.