States that do very little testing might show very few lead poisoning cases — which can create the appearance of safety but actually reflects a lack of data. Washington, for example, has had historically low levels of lead screening with only about 1 percent of all children there getting tested.
Cunningham and his colleagues built a map meant to show both parents and health providers the places where they should be most concerned about the possibility of kids experiencing lead exposure.
"The ultimate goal is to make sure we're testing the kids who need to be tested," Elisabeth Long, also an epidemiologist with Washington, says. "This helps us start taking public health actions, and prevent other kids from exposure."
Knowing about high-risk areas is important. But what are the side effects of knowing?
There are certain challenges that come along with discussing lead risk — and that might explain why it's an area that health departments have not approached aggressively.
One is that high-risk scores don't correlate perfectly with an individual's chance of exposure. There are kids who live in the high-risk areas who might be just fine — they might live in a brand new house, for example — and children in low-risk areas who could still be harmed by exposure to lead.
"It's a hard message when you're talking about lead exposure," Long says. "And we don't want to be alarmist, but also [we want to] give more people more information about where they live."
Sometimes health departments can be reticent to single out a specific area as "high risk," as it could pose economic harm if other families or businesses don't want to move there.
"One worry you can have is about a domino effect, where businesses may decide to pull out in high-risk areas or real estate prices go up in the lower-risk areas," APHA's Patel says. She still thinks it's better to make this type of information public, even though it does carry some of these risks.
There are also limitations to how much epidemiologists can do to map risk. There are other factors that studies have associated with lead risk — whether there has historically been a local lead smelting plant, for example. But this map doesn't take that factor into account, because the data on where those plants are isn't as robust as data on poverty and housing age, which the federal government tracks closely.
While the data is relatively granular, pointing to how high the risk level in your specific geographic area might be, it still does not tell us which specific houses could expose children to lead.
"One challenge is that there is huge variability from neighborhood," says David Jacobs, chief scientist at the National Center for Healthy Housing. "What would be even more preferable is finding the exact houses where lead exists."
What this map tells us: Lead exposure risk is greatest in urban areas and less common in Western states
This map identifies the places where kids would experience the highest and lowest risks of lead poisoning. It does that by taking all 72,241 census tracts and assigning them a risk score between 1 and 10, based on how old the local houses are and the percentage of the population living in poverty.
Each grouping represents 10 percent of the total number of census tracts, so within each risk level (all the dark blue census tracts with a 1, for example) there is some variation. But what this map does especially well, as Cunningham explained, is identify the hotspots for lead exposure.