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America does a terrible job tracking how many kids have lead poisoning

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In the wake of Flint, Michigan's lead poisoning crisis, I've spent the past few weeks researching how widespread an issue elevated blood lead levels are in children.

It hasn't been easy. We know that even low levels of lead in the blood can reduce IQ and affect the ability to pay attention. We know that lead can cause irreversible neurological damage. Some researchers even think it's associated with the mid-1990s spikes in teen crime.

We know that lead is a problem — but it's nearly impossible to know how much lead exposure kids in a certain zip code, neighborhood, or census tract might come in contact with. If you're a parent who wants to know whether kids in your area are especially at risk for lead poisoning, I can tell you from my research that it won't be easy.

Let's say, for example, you live in California. You'd see on the Centers for Disease Control and Prevention site data about lead elevated blood level rates there for 2014. It wouldn't have any sort of geographic breakdown available— something that's important for a state with 38 million people.

But it turns out that page isn't really data for California. It's only data for Los Angeles County. I only know that because I spoke with someone involved in Los Angeles's childhood lead surveillance program. And when I spoke with a representative at the CDC about the missing data, she was polite, but said I'd just have to contact the state health department if I wanted to learn more. (After that phone conversation, it appears the CDC updated California's state data page to show that the 2014 data is just an excel file of LA County's numbers).

And this isn't just California. My experience reporting on lead exposure nationwide suggests that our monitoring of lead exposure is hugely inadequate — even though it remains a significant problem, especially in the country's most vulnerable communities.

Blood lead levels have dramatically decreased, but there is still a national problem

In 1984, 17 percent of all American preschool children had blood lead levels that exceeded 15 micrograms per deciliter of blood. But thanks to the ban of leaded paint in 1978 and the gradual phaseout of leaded gasoline in the mid-1970s, BLLs in preschool children have continued to decline, so that in 2014 just 0.53 percent of children tested in the US had blood lead levels of 10 μg/dL or greater. This is a huge public health success story — but also not a complete victory.

Lead concentration of 10 μg/dL or greater in the bloodstream is incredibly toxic and requires immediate intervention and case management. But studies have linked even lower levels of exposure — as low as 2 μg/dL — to reduced IQ in children.

The CDC knows this, and in 2012 it updated its own recommendations to establish 5 μg/dL as the new threshold used to identify children with elevated blood levels, stating that this level of lead in the bloodstream indicates "these children are exposed to more lead than most children."

In 2014, 0.53 percent of children tested in the US had blood lead levels of 10 μg/dL or greater. But 4.2 percent of children tested positive for 5 μg/dL or more in the bloodstream. That means there are thousands of children in the United States with lead exposure above the federal threshold.

Another question you might have looking at the data provided by the CDC is why only 2.5 million kids were tested if the population under 5 years old in the US was 24.3 million. In other words, why was just over 10 percent of the population tested?

That's largely because blood lead level testing is not required, and often only the most vulnerable children are tested, which is why the number of children tested at the city, county, or state level can vary dramatically depending on where you look.

The map above uses 2014 CDC data to show elevated blood lead levels in the range of 5 μg/dL to 9 μg/dL in counties across the country. But the reason so many of the counties are light gray is that most counties simply don't share this information with the CDC — nor are they required to.

Twenty-one states do not regularly submit data to the CDC on lead surveillance programs in their states. Eleven of those 21 states do not submit any kind of lead surveillance data to the CDC — no state-level or county-level data. The other 10 states do submit some data, but many haven't submitted anything in the past two years. For instance, North Carolina hasn't submitted its data since 2009.

The CDC did spend $11 million in 2014 to fund lead surveillance programs for three years in 29 states and six cities (including the District of Columbia). And those states are the ones that are required to send the government data.

But even those data sets aren't comprehensive — look at Louisiana or Oregon, for instance — or, as I learned in the case of two counties in Alabama, if it's not missing it's incomplete and inaccurate.

Earlier we reported that Houston County and Dallas County in Alabama had some of the highest rates of elevated blood levels (in Houston County, it was 58 percent), but the number of children tested was small. Houston County only tested 12 and Dallas County only 19.

That means the blood level rates of children were calculated by Alabama public health officials using incredibly small sample sizes without any explanation as to why. Small sample sizes are problematic because they are not representative of a larger population, making it nearly impossible to draw decisive conclusions.

I started to get conflicting information about which kids would even get tested in the first place. After I wrote about Houston County, a retired Alabama government official who worked closely with the lead surveillance program emailed me to say the state only tests kids they suspect have been exposed to lead.

Alabama's public health department declined to comment on who was tested, later issuing a press release that said testing was done "at the discretion of the doctor."

The press release clarified that only cases with lead levels of 10 μg/dL or higher required reporting. The statement said that while it recommended physicians to report cases with lower blood lead levels of 5 to 9 μg/dL, it wasn't mandatory.

This all gets back to the difficulty of getting good data on lead exposure in the United States. There are no standards of what information gets reported or which children get tested. I still don't have a clear answer on how well Alabama's numbers represent lead exposure in that state — and that's after talking directly to public health officials there about how the system works.

We know lead poisoning impacts communities disproportionately, but we don't know the full extent

Generally speaking, the CDC knows that children from poorer families are generally more at risk for lead poisoning and that communities of color are impacted unequally. For instance, a 2013 study from the CDC found that black children had twice the amount of elevated blood lead levels as their white counterparts.

But if we look at neighborhood areas in New York, we can see it's not just race or poverty that make a community susceptible to elevated blood lead levels.

Neighborhoods in Brooklyn — in particular, Greenpoint — had the highest rates of children test positive for more than 10 μg/dL in the bloodstream. In Greenpoint, 1.17 percent of children tested positive. In Borough Park (also in Brooklyn), it was 0.54 percent.

Both Greenpoint and Borough Park are poorer areas of the city, with 22.5 percent and 32.1 percent of the population living in poverty, respectively — but areas in the Bronx that have similarly high levels of poverty reported lower levels of lead in the bloodstream.

In Pennsylvania, the department of health maintains a list of 20 cities that are known to experience greater rates of elevated blood lead levels than the rest of the state, but the cities vary dramatically in demographics.

According to classifications determined by the Center for Rural Pennsylvania, four of the 20 cities are located in rural counties, and the other 16 are in urban counties. For instance, Johnstown is located in the rural county Cambria but reported that 18.26 percent of 690 children tested had BLLS of 5 μg/dL or greater — higher than the percentage in Philadelphia, at 10.19 percent.

There is no standard for how states should administer their childhood lead surveillance programs, and testing isn't mandatory, despite the fact that the CDC has said "no safe blood level in children has been identified."

In the coming weeks, I'm going to continue to delve more deeply into these issues, to try to paint as complete of a national picture as possible. Please feel free to email me with tips and advice.