Nearly a quarter of infants in the Chinese capital Beijing consumed milk formula tainted with melamine before the products were withdrawn from sale.
The official Xinhua newsagency says more than 307-thousand Beijing families with children under the age of three were screened.
It says the survey by the Beijing Municipal Health Bureau found that more than 75-thousand babies had been fed contaminated milk formula.
Four children have died and thousands of others have fallen ill from drinking milk formula adulterated with melamine, which was subsequently found in other drinks and foods.
The issue has led to Chinese-made products being pulled from shelves worldwide.