Mari Copeny, 8, of Flint, Mich., waits in line to enter a Capitol Hill hearing room where Michigan Gov. Rick Snyder (R) and Environmental Protection Agency Administrator Gina McCarthy were to testify in March. (Kevin Lamarque/Reuters)

The ill-fated decision two years ago to switch drinking-water sources in Flint, Mich., resulted in a sudden spike in the number of young children with elevated blood lead levels, according to data released Friday by the Centers for Disease Control and Prevention.

Public health officials have long known that the city's water crisis left nearly 9,000 children 6 and younger exposed to lead, a toxic contaminant that can cause permanent learning disabilities, behavioral problems and, at higher levels, a number of diseases. But to better understand the impact Flint's tainted water had on the city's most vulnerable population, CDC officials looked at lead tests before, during and after the switch.

Researchers found that Flint children had a 50 percent higher chance of having elevated blood lead levels after the switch in 2014. After the city switched back to Detroit water in late 2015, the percentage of children with elevated blood lead results "returned to levels seen before the water switch took place," the agency said.

"This crisis was entirely preventable, and a startling reminder of the critical need to eliminate all sources of lead from our children's environment," Patrick Breysse, director of the CDC's National Center for Environmental Health, said in a statement Friday.

The lead problems in Flint’s water began after the city switched to the Flint River for its water supply beginning in April 2014, as part of a cost-cutting move. State regulators failed to ensure that anti-corrosion chemicals were added to the water, which became contaminated when lead leached into it from aging underground pipes. The city eventually switched back to Detroit water in October 2015.

While there is no level of lead in the blood that is considered safe, CDC considers anything greater than five micrograms per deciliter as a "level of concern." Public health officials continue to recommend that all children under age 6 living in Flint have their blood tested for lead.

Friday's study had some limitations. For example, researchers were not able to account for exposure to lead-based paint or other potential environmental sources that could have exposed children to the toxic substance. In addition, researchers lacked information about the precise amount of lead-tainted water consumed by individual children, which limited their analysis to evaluating changes in the results of blood tests over time as the city's water source changed.

The CDC's work builds on initial findings from local pediatrician Mona Hanna-Attisha, who played a major role in bringing Flint's lead crisis to the public spotlight. In August 2015, she was startled by what she found when looking back over the lead tests of 1,750 children taken at a local hospital.

“We found that when we compared lead levels before and after the [water] switch, the percentage of kids with lead poisoning doubled after the switch,” she told The Washington Post in an interview earlier this year. “In some neighborhoods, it tripled. And it all correlated with where water lead levels were the highest.”

Hanna-Attisha and several colleagues released the results at a news conference in September 2015, but the backlash was swift. State officials questioned the findings and accused Hanna-Attisha of causing unnecessary hysteria. The state later agreed that her figures were accurate.

The episode, Hanna-Attisha said, has caused a “community-wide trauma” in a city ravaged by crime, poverty and widespread unemployment.

“Our families are already riddled with every possible stress,” she said. “Every obstacle to a kid’s success, we already had. . . . And then they gave a population lead poisoning.”

In April, researchers from Virginia Tech said Flint’s water system is in far better shape since the city switched its water source in the fall and began adding chemicals to control the corrosion of aging pipes. But they made it clear that the threat of lead contamination remains.

This week, the federal government lifted a recommendation that pregnant women, nursing mothers and children under 6 in Flint drink only bottled water.

The advice was based on tests of filters that have been distributed for months for free by the state of Michigan. The Environmental Protection Agency has been testing water from the filters and has said they remove or reduce lead well below the federal action level of 15 parts per billion.

President Obama drank filtered water several times during a visit last month to Flint.

"It confirms what we know scientifically that if you use a filter ... then Flint water at this point is drinkable," he said. "That does not negate the need to replace some of those pipes, because ultimately we want a system where you don't have to put a filter on it."

Federal officials said they have provided millions of gallons of bottled water to the state of Michigan, along with more than 50,000 water filters. Government aid has included expanding medical services to thousands of Medicaid-eligible pregnant women and children.

This post has been updated.

Correction: An earlier version of this post misspelled the name of the CDC's Patrick Breysse.

The crowd went wild during President Obama's speech in Flint, Mich., on May 4, when he asked for a glass of water, which took several minutes to acquire. Flint residents can only drink filtered tap water after a crisis involving dangerous levels of lead in the water system. (Reuters)

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