Urinary tract abnormalities in Chinese rural children who consumed melamine-contaminated dairy products: a population-based screening and follow-up study

Background

Kidney damage related to consumption of melamine-contaminated dairy products by young children in China has been described. However, no studies have reported on the population-based prevalence of kidney damage among exposed children or on the condition of affected children after follow-up.

Methods

We conducted an ultrasound-based screening in September 2008 of 7933 children younger than 36 months of age who lived in a rural area in China where the dairy products most highly contaminated with melamine were sold. We monitored children who had evidence of nephrolithiasis or hydronephrosis at screening using renal ultrasonography after one, three and six months. We also collected information from the mothers of affected children about consumption of melamine-contaminated products between June and August 2008.

Results

The overall prevalence of urinary tract abnormalities among screened children was 0.61% (95% confidence interval CI] 0.45%–0.80%). The mean exposure dose of melamine was estimated to be 116 (range 36–220) mg per day. Of the 48 affected children, 43 (89.6%) were asymptomatic, 2 had symptoms and were hospitalized, and 3 had symptoms but treatment had been not sought for them. Of the 46 children for whom six-month follow-up information was available, renal abnormalities persisted in 5 children and resolved in the remaining 41.

Interpretation

Among children who underwent screening, 0.61% showed ultrasonographic evidence of nephrolithiasis or hydronephrosis. Most of the affected children were asymptomatic. The majority of the affected children recovered from the toxic effects of melamine over time without specific treatment. Renal abnormalities remained in 12% of the affected children.Contamination of dairy products with melamine in China has resulted in a widespread outbreak of serious kidney damage in children.^1–4 On Sept. 12, 2008, the Chinese government announced to the public that the outbreak had occurred and initiated various emergency responses, including the set-up of a high-level national coordinating group, free screening and treatment of affected children, thorough inspection of all dairy products and producers, timely release of information to the public, recalls of contaminated products, suspension of production of the contaminated milk and compensation to the families of affected children. More than 50 000 children have been hospitalized and six have died because of kidney damage.⁵Melamine is a nitrogen-containing compound commonly used in chemical industry. Because its addition to milk elevates apparent protein content, raw milk was intentionally adulterated with melamine in the production-chain, leading to contamination of dairy products and high-level exposure of thousands of children.⁶Melamine is known to cause formation of calculi in weanling rats and has led to acute renal failure in cats and dogs consuming melamine-contaminated pet foods.^7,8 In humans, melamine-related disease has been recognized only recently, and the full adverse effects of exposure remain unknown.^4,9 A clinicopathologic study suggests that the size of urinary stones is related to melamine concentration.⁹ A recent hospital-based study in Beijing reported the prevalence of nephrolithiasis was 8.5% among children who were exposed and referred by other hospitals.¹⁰However, no studies have reported on the population-based prevalence of kidney disease among exposed children, nor have follow-up reports been released about affected children. We performed a population-based screening and follow-up study involving residents of a rural area situated close to the manufacturer of Sanlu dairy products, which was the source of the most severely melamine-contaminated products in the mainland of China.¹¹ The study was approved by the Institutional Review Board of Peking University.