Air pollution may impact timing of asthma seasons
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The traditional calendar dates for spring, summer, winter and fall did not correlate with asthma seasons, which often are driven by air pollution, according to research conducted in South Carolina and published in PLOS One.
The study researchers charted ED visits resulting in a primary diagnosis of asthma among children aged 5 to 19 years residing in South Carolina from 2005 to 2014 to determine when asthma seasons occur and how they correlate with seasonal burdens of ambient air pollutants.
“It happened somewhat organically, although we knew we wanted to detail the environmental factors associated with spatial and temporal patterns in asthma ED visits,” study researcher Matthew Bozigar, PhD, a postdoctoral associate in environmental health at Boston University School of Public Health, told Healio.
Using high-resolution data on air pollution and ED visits for asthma among 66,092 children (58.5% male; 68% African American; 46.9% aged 5-9 years) living in South Carolina, the researchers conducted a precise spatio-temporal analysis.
“We initially thought that spatial patterns would be most important, but we quickly realized that there were strong temporal patterns in asthma ED visits in South Carolina and decided to explore that further,” Bozigar said.
Researchers found that the winter asthma season, defined by much cooler temperatures and a medium burden of 16.5 ED visits a day, ran from Jan. 1 to the end of February. The burden increased between March 1 and May 31 as temperatures fluctuated but also rose, with 18.9 ED visits a day.
The burden receded between June 1 and Aug. 19 while children were out of school, with 9.4 ED visits a day. But the fall asthma season began on Aug. 20 as children returned to school and temperatures were still warm before gradually cooling, with 23.5 ED visits a day, through Dec. 31.
“Rhythms in asthma quite simply do not appear to follow traditional seasonal markers. There is a strong back-to-school spike in adverse asthma outcomes that is likely a reflection of viral circulation and infection, for example,” Bozigar said.
Given asthma’s multifaceted nature affected by indoor and outdoor factors, Bozigar said that it makes sense that if those underlying factors do not follow strict seasonal definitions, then neither would asthma ED visits.
“We should therefore move away from typical seasonal definitions to understand temporal patterns,” he said.
Course particulates (particulate matter < 10 m and > 2.5 m: PM10-2.5) and nitrogen oxides (NOx) may contribute to asthma ED visits throughout the year, according to the researchers, but burdens vary by season.
The researchers found increased odds — measured by the odds of an interquartile range increase or decrease (ORIQR) — for an ED visit from elevated levels of NOx (ORIQR = 1.018; 95% CI, 1.002-1.032) and PM10-2.5 (ORIQR = 1.054; 95% CI, 1.026-1.063), although air pollutants were not significantly associated with ED visit odds during the winter and spring asthma seasons.
But during the fall asthma season, researchers observed positive statistically significant associations between asthma ED visits and NOx (ORIQR = 1.034; 95% CI, 1.009-1.06) and PM10-2.5 (ORIQR = 1.144; 95% CI, 1.114-1.177).
In other words, the researchers wrote, the magnitude of the association between asthma ED visits and PM10-2.5 was nearly three times greater in the fall asthma season compared with the entire year.
“We did not expect to find a strong association with coarse particulate matter. Many more studies have linked asthma exacerbations and ED visits to small particulate matter than coarse particulate matter because small particles can embed deeper in the airways and lungs,” Bozigar said.
Additional research could reveal the reasons behind this association between ED visits and coarse particulate matter, Bozigar continued, as well as why the relationship only appears in the fall and whether the composition of the mixture plays a role.
The researchers further believe that the results of this study may be consistent for states that are similar historically, geographically, climatically, and demographically.
“Although additional research is needed to confirm, we suspect results may be similar in neighboring states North Carolina and Georgia,” Bozigar said. “However, most states do not have statewide ED visit data, which we were able to obtain through a close partnership with the South Carolina Revenue and Fiscal Affairs Office.”
Despite these findings, the researchers are hesitant to make any direct clinical recommendations to clinicians without additional research.
“However, clinicians may be able to help patients better understand their asthma symptoms by inquiring about individual triggers at multiple timepoints, across visits to the health care system,” Bozigar said.
“Systematizing questions about asthma triggers in electronic health records could better integrate research and clinical objectives alike, though it would take a coordinated effort among a diverse set of stakeholders,” he added.
The researchers are continuing their work as well.
“With another team, we are currently using electronic health records to analyze other environmental exposures, including those indoors related to housing, allergens and indoor air pollution and their influences on asthma,” Bozigar said. “Again, because it is a multifactorial disease, as researchers there are many pieces to try to put together to complete the asthma picture.”
For more information:
Matthew Bozigar, PhD, can be reached at bozigar@bu.edu.