Objective To investigate the risk factors of infantile urolithiasis resulted from taking milk powder with melamine. Methods The clinical data of infant and young children who took free-screening for melamine associated urolithiasis in the Lanzhou University Second Hospital from September 14th, 2008 to January 6th, 2009 were collected, while the infants without urolithiasis in the same number as those with urolithiasis were also randomly collected into the control group. Then both univariate and multivariate analyses were performed with a logistic regression model to assess the independent risk factors for urolithiasis. Results Of the screened children, 647 children were included in the urolithiasis group and 647 were in the control group. There were 678 boys and 616 girls with an average age of 19.27 months. The results of logistic regression analysis showed that, the children fed with Sanlu powdered infant milk formula which contained a high level of melamine were more likely to suffer from urolithiasis than those took other melamine-contaminated formula (OR=6.09, Plt;0.01); boys were more than girls (OR=1.39, Plt;0.01), and children fed with formula alone were more than those fed with both formula and breast milk (OR=1.61, Plt;0.01). The risk of urolithiasis decreased gradually with age, and the OR value of children in age of smaller than 6 months, 6 to 12 months, 12 to 24 months were 5.23 (Plt;0.01), 2.73 (Plt;0.01), and 1.60 (Plt;0.01), respectively. The risk of urolithiasis increased gradually with the time lengthening of taking melamine-contaminated formula, and the OR value of children who had took melamine-contaminated formula for 3 to 6 months, 6 to 12 months and more than or equal to 12 months were 2.10 (Plt;0.01), 2.81 (Plt;0.01), and 4.75 (Plt;0.01), respectively. Conclusion It shows that feeding with high melamine infant formula (Sanlu powdered infant milk formula), artificial feeding and male children are the risk factors of infantile urolithiasis. Additionally, the risk of urolithiasis decreases with age and increases with time of formula feeding
