Air pollution tied to increased hospitalization among children with Autism: A time-series study

South Korea: A recent study published in BMJ Open emphasized the consideration of reducing exposure to air pollution to manage symptoms of Autism Spectrum Disorder (ASD). The primary connotation is the quality of the patient's life and family members and the economic costs involved in treatment and care.

ASD is a neurodevelopmental disease signalized by a deficiency of social communication, constricted interests, and repetitive behavior. This major public health problem is prevalent in the USA and the Republic of Korea. The disease requires high lifelong support costs, US$2.2 million in the USA and US$2.4 million in the UK.

ASD accompanies neuroinflammation and systemic inflammation. The severity of ASD is associated with levels of serum inflammatory cytokines, and the ASD symptoms can be improved by modulating inflammation. As a result of exposure to short-term air pollution, inflammation is induced due to particulate air pollutants penetration through the lungs and olfactory epithelium, blood-brain barrier changes, and microglia activation, thereby aggravating ASD symptoms.

There are studies focussing on the association between long-term exposure to air pollution during pregnancy and the development of ASD among children, but the evidence is incomplete.

Against the above background, a time-series study was conducted by Kim et al. and the team from the Department of Preventive Medicine and Public Health of Ajou University School of Medicine and Institute of Public Health and Medical Care, Department of Neuropsychiatry of Seoul National University Hospital. This study explored the effects of short-term exposure to air pollution on hospitalization for ASD Korean children aged 5-14 years (cannot be diagnosed until 3 years) as a proxy for ASD symptom aggravation.

The study used data from National Health Insurance Service from 2011 to 2015. The exposure of interest in this study was daily concentrations of fine particulate matter (PM2.5), Nitrous dioxide (NO2), and ozone (O3) levels. PM2.5 levels were estimated using the Integrated Multi-Scale Air Quality System for Korea. The levels of NO2 and 03 were obtained from 318 fixed-site monitoring stations of the National Ambient Air Monitoring Information System.

To measure outcomes, the researchers applied distributed non-linear lag models and a generalized difference-in-differences method to the quasi-Poisson models to estimate the causal effects of air pollution for up to 6 days. Weighted quantile sum regression analyses analyzed the combined effects of air pollution mixtures.

The critical points of the study are:

• The observed mean daily count of ASD hospitalization was 8.5, the count being higher in boys (7.0) than girls (1.6).

• The means of daily mean PM2.5 was 19.3 µg/m3, NO2 level was 20.7 parts per billion (ppb), and daily 8 hours maximum O3 levels was 37.2 ppb.

• The relative risk was 1.17 for PM2.5 levels at lag day 1, associated with a higher risk of hospital admission for ASD.

• The relative risk was 1.09 for NO2 levels at lag day 5 and 1.03 for O3 levels at lag day 4, respectively, associated with a higher hospitalization risk for ASD. The risk was lower at lag day 0 for PM2.5 and NO2.

• The observed mean daily count for ASD hospitalization would be reduced to 7.3, 7.8, and 8.3 when there is a decrease in PM2.5 levels by 10.0 µg/m3, NO2 by 10 ppb, and O3 by 10 ppb, respectively.

• The mean daily count of hospital admission among boys would be reduced to 5.9, 6.5, and 6.4 when PM2.5 level drop by 10.0 µg/m3, NO2 by 10 ppb, and O3 by 10 ppb, respectively.

• The mean daily count among girls will be reduced to 1.5 when PM2.5 levels decrease by 10.0 µg/m3 and O3 by 10 ppb.

• There is a high risk of hospitalization for ASD when all the pollutants are together considered with a relative risk of 1.29. Nitrous oxide's contribution is the most, with a weight of 0.80

Short-term exposure to air pollution activates microglia, and the secretion of proinflammatory cytokines like interleukin-6 and tumor necrosis factor (TNF)-α marks the severity of communication impairment and aberrant behaviors among ASD children.

The first author and co-author mentioned that "short-term exposure to air pollution aggravates ASD symptoms more in boys than girls. This is related to increased microglia activation by testosterone and lowers glutathione and sulphate levels (antioxidant) among boys compared to girls."

The researcher mentioned a future perspective of analyzing the association between hazardous air pollutants (lead, mercury, arsenic) with aggravation of ASD symptoms.

Further studies are warranted for confirmation of results and draw policy implications, researchers wrote.

Reference:

Kim K-N, Sohn JH, Cho SJ, et al. Effects of short-term exposure to air pollution on hospital admissions for autism spectrum disorder in Korean school-aged children: a nationwide time-series study. BMJ Open 2022;12:e058286.