In low-income urban areas, decreases in air quality related to specific pollutants were significantly associated with nonviral exacerbations of asthma in children, a finding that led a team of investigators from the National Institute of Allergy and Infectious Disease to state that “air pollution is an important independent risk factor for” acute worsening of asthma in this population.
The team’s analysis also associated individual pollutants with changes in airway physiology and gene expression during exacerbations and linked those to distinct pathways of airway inflammation and decreased lung function.
“The negative effects of air pollution are likely to be particularly relevant in urban centres, where pollution exposure is high and the prevalence and morbidity of asthma in children is disproportionately high compared with rural and less dense urban areas,” wrote first author Matthew C. Altman, MD, from the University of Washington in Seattle, and colleagues in The Lancet Planetary Health.
While research on the physiologic effects of individual air pollutants is robust, the molecular mechanisms by which pollutants trigger asthma exacerbations are poorly understood, and particularly in susceptible populations, such as children with severe or uncontrolled asthma, added investigators. Moreover, asthma attacks provoked by respiratory virus infections -- a common trigger -- have been studied extensively, but those that occur independently of such infections have not.
The retrospective analysis evaluated data from the Secondary Assessment of Mechanisms Underlying Asthma Exacerbations Prevented and Persistent with Immune-based Therapy (MUPPITS MUPPITS1) cohort which enrolled 208 children with exacerbation-prone asthma aged 6-17 years from urban areas across 9 US cities. The study used air quality data to examine the impact of air pollution on cellular and physiologic mechanisms that contribute to disease severity.
Investigators then validated MUPPITS1 data in the Inner-City Anti-immunoglobulin (IgE) Therapy for Asthma (ICATA) cohort which included 419 patients with persistent allergic asthma, aged 6-20 years, living in urban areas across 8 US cities.
The final cohort for the current retrospective analysis comprised 168 participants (98 boys) from the MUPPITS1 and 189 from the ICATA (115 boys) cohorts.
Altman et al found that increased air quality index values that were driven primarily by elevated levels of particulate matter (PM2.5) and ozone (O3 )concentrations were significantly associated with nonviral exacerbations of asthma and decreased pulmonary function.
Individual pollutants were significantly associated with altered gene expression in inflammatory pathways, the authors report. Specifically, PM2·5 was associated with increased epithelial induction of tissue kallikreins, mucus hypersecretion, barrier functions and O3 with increased type-2 inflammation, the team reported.
"Our findings suggest that air pollution is…potentially linked to [asthma] exacerbations through specific inflammatory pathways in the airway," they add.
"These data add to the growing body of evidence supporting the need to reduce outdoor air pollution as a means to decrease respiratory illnesses and asthma-related morbidity in children living in urban areas," the authors write.They also suggest that novel asthma management strategies could be developed for youth in underserved communities, such as "personal air quality sensors and air filters to prevent pollution from entering the environment."
Reference: Altman, MC, Kattan M, O’Connor GT, et al. Associations between outdoor air pollutants and non-viral asthma exacerbations and airway inflammatory responses in children and adolescents living in urban areas in the USA: a retrospective secondary analysis. Lancet Planet Health. 2023;7:33-e44. doi:10.1016/s2542-5196(22)00302-