Across Los Angeles County, more than 15,000 children under 6 tested high for lead between 2011 and 2015, according to an investigation by Reuters. 323 neighborhoods were identified as having elevated levels of lead that were as high as the levels in Flint, Michigan.

The data gathered by Reuters reveals that lead poisoning across L.A. County affects affluent and poor neighborhoods. In San Marino, more than 17 percent of small children tested have shown elevated levels of lead in their blood, according to previously undisclosed L.A. County health data.

That far exceeds the 5 percent rate of children who tested high for lead in Flint, Michigan, during the peak of that city’s water contamination crisis.

“This is a very serious matter, and as the mayor, I really want to further explore it,” San Marino Mayor Richard Sun said upon reviewing the numbers presented by Reuters. During an interview at City Hall, he directed city officials to investigate potential sources of exposure.

Among the measures Mayor Sun wants to consider: An ordinance to ensure safe practices any time home repairs or renovations could disturb lead paint.

Despite decades of U.S. progress in curbing lead poisoning, millions of children remain at risk. Flint’s disaster is just one example of a preventable public health crisis that continues in hotspots coast to coast, Reuters has found.

Poverty is another predictor of lead poisoning, and many of L.A.’s danger zones are concentrated in low-income or gentrifying areas near downtown and on the city’s densely populated South Side.

In one low-income area of South L.A., Reuters met with the family of Kendra Nicole Rojas, a three-year-old recently diagnosed with lead poisoning, only to find that 63 other small children living within a six block radius have also tested high.

“A lot of people don’t even think of the West Coast as a place where kids get poisoned,” said Linda Kite, executive director at L.A.-based Healthy Homes Collaborative. “The biggest problem we have is medical apathy. Many doctors don’t test children for lead.”