Short-term air pollution exposure may be tied to child hospitalizations

More hospital encounters seen for SCD children but not adults in new study

Steve Bryson, PhD avatar

by Steve Bryson, PhD |

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A child is seen coughing amid clouds of pollutants.

Short-term exposure to air pollutants may be associated with a higher risk of hospitalization among children with sickle cell disease (SCD), according to a new study examining data from the southeastern U.S. state of South Carolina.

In particular, more so-called hospital encounters were seen in SCD children within two weeks of them being exposed to higher levels of industrially-generated ground-level ozone and elemental carbon produced from traffic-related emissions.

In SCD adults, however, no links between short-term exposure to air pollution and hospital encounters were identified.

While the scientists said further research is needed to confirm these findings, the study highlights that “sickle cell disease (SCD) may be sensitive to environmental stressors.”

Further, the team noted these “findings suggest that short-term (within two-weeks) levels of [elemental carbon] and [ozone] … may be associated with SCD hospital encounters among children.”

The study, “Short-term air pollution levels and sickle cell disease hospital encounters in South Carolina: A case-crossover analysis,” was published in the journal Environmental Research.

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Study focused on South Carolina patients with sickle cell disease

In SCD, a defective form of hemoglobin, the protein responsible for oxygen transport in the body, causes red blood cells to stiffen and become deformed. This compromises oxygen supply to various tissues and can lead to blood vessel obstructions, causing episodes of intense and sudden pain, known as vaso-occlusive crises (VOCs).

Studies suggest that certain environmental factors such as temperature and wind speed may trigger SCD complications. In other studies, short-term exposure to elevated levels of air pollutants has been shown to increase the risk of acute cardiovascular events, such as heart attacks.

However, whether short-term exposure to air pollution can be associated with worse SCD outcomes remains poorly understood.

To address this gap, a team led by researchers at Penn State College of Medicine, in Pennsylvania, examined the potential association between short-term air pollution exposure and acute SCD complications, using hospitalizations as a measure.

The team analyzed zip-code-based air pollution and administrative health data from 2002 to 2019 in South Carolina — a state with a high number of reported SCD-related complications and mortality.

The outdoor air pollutants investigated included ground-level ozone, elemental carbon, and particulate matter measuring less than 2.5 micrometers in diameter, or PM2.5.

Ground-level ozone comes from pollution emitted by cars, power plants, refineries, and chemical plants, while elemental carbon comes from traffic-related emissions and coal combustion. PM2.5 are fine particles that are about 30 times smaller than a human hair, and include dust, soot, ash, aerosols, and mold spores.

For each air pollutant, the average time — one, three, five, nine, and 14 days — before the date of an SCD-related hospital encounter was calculated and included in the analyses.

During the study period, 8,410 SCD patients were identified and a total of 144,129 hospital encounters were registered, including the initial encounter and readmission. Patients with one visit over the study period were excluded, as were those with visits occurring within seven days of the first encounter.

Most patients were Black individuals (96.6%) and nearly two-thirds were female (63.3%). More than three-quarters lived in an urban area (78.2%), according to demographic data. At the time of the hospital encounter, 61.1% were on public insurance.

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More risk seen for SCD children within 9-14 days of air pollution exposure

No statistically significant associations were found between any of the air pollutants and SCD hospital encounters in sickle cell disease patients of all ages, or among adults.

Among children, however, exposure to higher levels of ozone and elemental carbon, within an average of nine to 14 days, was significantly associated with more SCD hospital encounters. Co-existing medical conditions, urban or rural locations, or insurance payor status had no impact on the findings in children.

When the analysis was restricted to patients with VOCs, similar patterns were found for all three air pollutants and SCD hospital encounters.

A strong association between 14-day average ozone exposure and VOC-related hospital encounters was detected among children, but not with elemental carbon when examined over an average of nine and 14 days.

According to the researchers, “this is the first study in North America to use the case-crossover design” to look at air pollution exposure over the short term and hospital encounters in SCD.

“We found epidemiological evidence that short-term air pollution exposures were associated with a higher risk of hospital encounters among children,” the team wrote.