Air Quality May be Correlated with Fatal Asthma Exacerbations

A study that was published online as part of the ATS 2020 International Conference assessed correlations of ambient air quality, temperature, and relative humidity with fatal asthma exacerbations among children.

North Carolina Office of the Chief Medical Examiner records were obtained for all deaths of children aged five to 19 years that took place between January 1, 2001, and December 31, 2016, in North Carolina, for which the primary cause of death was identified as asthma. For each fatality, researchers linked modeled mean ambient concentrations of particulate matter ≤2.5 µm in aerodynamic diameter (PM_2.5), mean ambient concentrations of ozone (O₃) in parts per billion (ppb), mean ambient air temperature, and mean ambient relative humidity by where and when the death took place.

They evaluated the correlations between the environmental variables and asthma deaths with a case-crossover analysis comparing environmental characteristics of each fatality’s county and death date and on matched comparison days (days falling on the same days of the week in the same month and year as the asthma death). Three linear spline terms with knots at the 33rd and 67th percentiles were created for each environmental characteristic; same-day and one- to five-day lagged daily means were considered. The final metrics for each characteristic were determined by model fit of the univariate models.

The final models included PM_2.5 (four-day lag), O₃ (five-day lag), temperature (three-day lag), and same-day relative humidity. A total of 81 deaths among children were identified during the study period; most children (n=44; 54%) were male and black (n=66; 82%). More than half of deaths (n=46; 57%) occurred between October and March. In the final model, for every ppb increase in O₃ in the highest tertile, the risk of fatal asthma increased by 8% (odds ratio [OR], 1.08; 95% confidence interval [CI], 1.01-1.14). For every percentage increase in relative humidity in the highest tertile, the odds of fatal asthma increased by 16% (OR, 1.16; 95% CI, 1.05-1.28). The other analyzed relationships were weak, with 95% CIs largely overlapping unity.

“These results suggest that selected ambient environmental conditions might be associated with an increased risk of fatal exacerbations of asthma among children in North Carolina,” the researchers summarized.