Air pollution associated with length of hospital stays in pediatric asthma in the Bronx

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Key takeaways:

• Ozone concentrations exceeded EPA standards 42 times between 2017 and 2019.
• Daily PM2.5 mass concentrations varied from 0.1 µg/m3 to 26.7 µg/m3.
• Longer hospital stays may indicate more severe exacerbations.

Ambient particulate matter at the 2.5 µm scale and ozone pollution were associated with longer hospital stays for pediatric patients with asthma in the Bronx, according to a study published in Journal of Asthma.

These longer hospital stays may indicate more severe asthma exacerbations with direct, measurable effects on health and health care costs, Elissa B. Gross, DO, attending physician, division of hospital medicine, Children’s Hospital at Montefiore, and colleagues wrote.

Data were derived from Hardell J, et al. J Asthma. 2023;doi:10.1080/02770903.2023.2225607.

“Asthma disproportionately affects children in the Bronx. At the Children’s Hospital at Montefiore, we have the highest rates in all the city for asthma admissions to the hospital at about 2,000 per year,” Gross told Healio.

The researchers were interested in improving modifiable risk factors that will boost children’s health, Gross continued.

Elissa B Gross

“One of the modifiable risk factors is air quality,” Gross said. “There is little literature on how air quality affects hospitalization in children, so this study attempts to fill this gap.”

The retrospective chart review involved 1,920 children and adolescents aged 2 to 18 years admitted to Children’s Hospital at Montefiore in the Bronx between Jan. 1, 2017, and Dec. 31, 2019.

Also, the researchers reviewed daily 24-hour totals of particulate matter mass at 2.5 µm (PM2.5) and 8-hour maximum ozone (O3) concentrations at two sites operated by the New York State Department of Environmental Conservation in the Bronx from 2017 to 2019 provided in US Environmental Protection Agency Air Data pre-generated data files.

The researchers excluded 153 children who did not live within the study area from the cohort, which was 88.6% aged younger than 12 years, 58.2% boys and 51.6% Hispanic. These figures correlated well with 2020 census estimates for the Bronx, the researchers said.

Also, 49.3% were normal weight, 46.8% had not been exposed to tobacco smoke or electronic cigarette vapors, 45.8% had not received the influenza vaccine, 60% did not use an asthma controller medication and 17% had positive respiratory viral panel (RVP ) results.

The daily mean length of stay was 2.07 days (standard deviation [SD], 1.27), and the mean number of hospitalizations was 2.2 admissions per day (SD, 1.41). Mean lengths of stay included:

• 2.24 days for girls and 2 days for boys (P = .001);
• 2.3 days for patients with persistent asthma and 1.92 days for patients with intermittent asthma (P < .001);
• 2.34 days for patients who used an asthma controller medication and 1.94 days for those who did not (P<.001);
• 3.25 days for patients who had a positive RVP result and 1.86 for patients with a negative RVP result (P < .001);
• 2.38 days for patients aged 13 to 18 years and 2.06 for patients aged 2 to 12 years (P = .007);
• 2.2 days for patients who had received the influenza vaccine, 2.14 for those who had not and 1.9 for patients with unknown vaccination status (P = .007);
• 2.15 days for patients with Medicaid insurance and 1.97 for those with other insurance (P = .03);
• 2.13 days for patients exposed to tobacco smoke or electronic cigarette vapors, 2 days for patients with no exposure and 2.11 for patients with unknown exposure (P = .032); other
• 2.2 days for patients with overweight, 2.01 days for patients with normal weight and 2.11 for patients whose weight was unknown.

There were no differences based on race or ethnicity, the researchers said. Also, the researchers said that the correlation between the measurements taken at the two pollutant monitoring sites was good (Spearman correlation coefficient > 0.8).

The researchers further said there was a strong seasonal pattern with higher O3 levels in the summer, including 42 days where the 8-hour O3 mixing ratio exceeded the EPA’s 70 parts per billion by volume (ppbv) standard with a high of 102 ppbv.

Daily PM2.5 mass concentrations varied from 0.1 µg/m3 to 26.7 µg/m3. The mean was 6.8 µg/m3 (SD, 3.9). Levels were slightly higher in the winter, the researchers said, although there were a few high PM2.5 events in the summer.

Longer lengths of stay were associated with higher levels of PM2.5 and lower levels of O3, the researchers said. Specifically, the researchers said, there was a positive effect with PM2.5 on the day of admission (Spearman correlation coefficient = 0.097; P = .0001).

Also, the researchers said, there was a weak positive effect on length of stay with PM2.5 on the day of admission and a slight decline for subsequent lag days (P < .001). O3 had a weak negative correlation as well, the researchers continued, with a statistically significant effect for lag3 day (P < .001).

The variations in length of stay with multiple demographic factors prompted the researchers to conduct additional analysis, finding a 9.48% increase in length of stay with each 10 µg/m3 increase in PM2.5 exposure on the day of admission.

“This means as air quality worsens, the asthma exacerbation has worsened. This 10% increase in LOS could mean another full day in the hospital,” Gross said. “This means increased hospital costs, increased lost workdays and school days for children. This can have a cumulative effect on a child’s health as well as significant socioeconomic impact.”

There was a 2.31% increase in length of stay with each 10 ppbv increase in O3 on the day of admission (95% CI, 0.28-19.52), the researchers said, but they did not consider this statistically significant.

However, the researchers continued, each 10 ppbv increase in O3 concentration on the day before admission was associated with a 3.9% increase in length of stay (95% CI, 0.06-7.88), which was statistically significant.

This effect increased slightly in two-pollutant models for PM2.5 (10.62%; 95% CI, 0.78-21.41) and O3 (3.01%; 95% CI, –0.81 to 6.98), but the researchers did not consider the change with O3 to be statistically significant.

Based on these findings, the researchers concluded that ambient PM2.5 levels on the day of admission and O3 levels on the day before admission may impact the length of stay for children and adolescents with asthma admitted to the hospital.

Whereas O3 levels exceeded EPA standards, the researchers noted, the daily and annual PM2.5 mass levels were below standards. But up to 20% of the students in pre-kindergarten through eighth grade in the Bronx attend a school within 150 meters of a major highway, and 30% attend a school within 150 meters of a highway or truck route.

Since these exposures are higher than other ambient background concentrations, the researchers said, the PM2.5 levels that these children are exposed to may be substantially higher than those recorded at the monitoring sites, indicating an even stronger association between length of stay and PM2. 5 levels.

The researchers called for additional research to assess the impact of air pollution on these populations as well as to investigate methods for mitigating asthma exacerbations impacted by air pollution. Meanwhile, Gross said, these results are probably not unique.

“I would expect similar results in large urban areas with populations and environmental conditions similar to the Bronx,” Gross said, adding that she would be interested in comparing the Bronx to results from other cities.

Physicians also should take these results under advisement in communicating with their patients.

“Physicians can recommend children avoid going outside on poor air quality days and say we know that this may increase their asthma exacerbation as well as if they need to be hospitalized, they may need to stay longer,” Gross said.

Additionally, physicians can take action beyond their own patients, Gross suggested.

“We as pediatricians should be advocating for improved air quality standards. I think these results could help policy makers further fight for cleaner air standards. Poor air quality has far reaching health effects and socioeconomic impact,” she said.

“By improving standards, we may be able to shorten the time children spend in the hospital,” Gross continued. “This will allow parents to work, contributing to the economy.”

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