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Kids With More Lead in Their Blood Faced Higher Odds of Strep Throat
In A Nutshell
- Kids with blood lead levels below the CDC’s action level still had more than double the odds of a strep throat diagnosis.
- Odds climbed higher still among kids at or above that level.
- No link to croup appeared, possibly because very young kids were often untested before falling ill.
- Records from 13,221 Philadelphia children show an association, not proof that lead causes strep throat.
Children with blood lead levels below the federal action level, the point where doctors recommend follow-up care, still had more than double the odds of a strep throat diagnosis, compared with kids who had the lowest levels, according to a study of 13,221 Philadelphia children. Among kids at or above that line, the odds climbed higher still.
Strep throat is a routine reason for kids to see a doctor, accounting for about 9 of every 100 outpatient visits and roughly 5 of every 100 antibiotic prescriptions among U.S. children ages 3 to 9, according to figures cited in the paper. An estimated 500,000 children ages 1 to 5 in the United States have unsafe lead levels in their blood each year. If lead from old paint and water pipes could be adding to strep infections, that changes the conversation about what counts as a safe amount of lead in a child’s bloodstream.
Researchers from Temple University and the University at Buffalo reported the results in the Journal of Exposure Science & Environmental Epidemiology. Authors say the strep findings support the conclusion that “no level of lead exposure is safe.” The work relied on existing medical records, not a new experiment, so it shows a pattern, not a cause.
Lead Exposure and Strep Throat Odds Rose Together in Kids
Researchers dug into patient records from Temple University Health System, a hospital network that serves many North Philadelphia residents, instead of recruiting new volunteers. All of the children were 14 or younger, were treated between 2010 and 2020, and had at least one blood lead test on file. A test counted only if it came before any strep or croup diagnosis, and kids with several tests were counted by their highest reading.
Children were sorted into three groups by lead level, measured in micrograms per deciliter: under 1, 1 to 3.4, and 3.5 or higher. That top cutoff is the action level the Centers for Disease Control and Prevention set in 2021, which the authors describe as “a public health screening and intervention threshold rather than a health-based safety threshold.” Roughly 28% of the children landed at or above it.
Adjustments covered each child’s age at the lead test, race, ethnicity, and insurance type, and boys and girls were also analyzed separately, with similar results.
Compared with kids in the lowest group, those in the middle group had 2.45 times the odds of a strep diagnosis, and those in the top group had 2.74 times. Odds, a close cousin of likelihood, weigh how many kids in a group had strep against how many did not. Strep also came back again and again more often as lead levels rose, at roughly two and a half times the rate in both of the higher groups.
Croup Showed No Link to Lead, Unlike Strep Throat
Croup, a viral illness common in young children, showed no meaningful connection to lead at any level. A testing gap may be the reason. Children in this system were screened for lead at ages 1 and 2, and croup tends to strike very young kids, many of whom may not have been tested before falling ill. That gap may have made a possible connection harder to spot, so the lack of a link does not prove lead has no effect on croup.
Strep Throat Links to Lead Were Strongest Among Black and Hispanic Kids
When results were split by race and ethnicity, the largest associations showed up among Black and Hispanic kids. Black children in the middle lead group had 3.56 times the odds of strep compared with Black children in the lowest group, and Hispanic children in the middle group had 2.87 times the odds compared with Hispanic children in the lowest group. Each comparison stays within one group, so the numbers do not show that one group is more vulnerable than another.
Aging Philadelphia Housing Raises Lead Exposure Risk
Philadelphia counts among the nation’s poorest cities, the authors say, with 21.4% of residents living in poverty in 2024, per U.S. Census Bureau figures. Most childhood lead exposure comes through household dust, paint, drinking water, and food, and aging homes often contain both lead-based paint and lead-contaminated dust. Poor upkeep in struggling neighborhoods adds further to the risk, and historic smelter sites and widespread demolition have widened lead exposure gaps in low-income Philadelphia areas, the authors note.
Why would lead leave kids more prone to strep? Lead has no role in the body, and the authors propose it may disrupt immune system development, which continues from before birth through the second year of life. That window overlaps with a period of high susceptibility to lead. A weaker immune response could make common infections like strep easier to catch, though that explanation remains unproven.
Kids below the CDC’s action line still faced higher odds of strep, so staying under it does not mean lead is harmless. Larger studies that track children over time will show whether the pattern holds, and whether the line sits in the right place.
Disclaimer: This article is for general informational purposes only and is not medical advice. The study reports an association and does not prove that lead exposure causes strep throat. Questions about lead exposure or a child’s health should go to a qualified health care professional.
Paper Notes
Limitations
The authors describe several limits. Every child came from one health system in one city, and the group was fairly homogeneous, so results may not apply to other communities. Lead data was missing for some croup cases, which may explain why no croup link appeared. The researchers could not fully account for secondhand smoke, body mass index, maternal education, number of previous births, or other environmental exposures such as air pollution. When body mass index and secondhand smoke were added to the analysis, the strep odds rose to 4.78 and 5.12, but only 5,605 children had that data, so the estimates were far less precise. The main models adjusted for age at the lead test, race, ethnicity, and insurance type, with sex examined in separate analyses. The repeat-diagnosis rate ratios were 2.39 for the middle group and 2.65 for the top group. Because the study relied on existing records and diagnosis codes, illnesses could be misclassified, and the records did not show whether blood was drawn from a vein or a fingertip. The authors expect such errors would weaken rather than exaggerate the associations. Race and ethnicity breakdowns were follow-up analyses, and as an observational study the work cannot show that lead causes strep throat.
Funding and Disclosures
The authors declare no competing interests. The paper does not list a funding source. It acknowledges three master of public health students, Sonia Habel, Carter Pason, and Nitzana Spiegel, who began the work with Dr. Marina Feiler at Temple University. The research was approved by institutional review boards at Temple University and the University at Buffalo, which waived informed consent because the study used existing medical records.
Publication Details
The study, titled “Environmental lead exposure and clinical infectious respiratory disease in a sample of urban and disadvantaged children,” was written by Eva Odiko and Rebecca Stutz (equal contributors), Jing Nie, Heather K. Lehman, John Turella, Adil I. Khan, and Marina Oktapodas Feiler, the corresponding author. Authors are affiliated with the University at Buffalo and Temple University. It was published online September 19, 2026, in the Journal of Exposure Science & Environmental Epidemiology as an open access article under a Creative Commons Attribution 4.0 license. DOI: https://doi.org/10.1038/s41370-026-00978-0
