Short-term, lagged association of airway inflammation, lung function, and asthma symptom score with PM2.5 exposure among schoolchildren within a high air pollution region in South Africa.

Background: Asthma affects millions of people globally, and high levels of air pollution aggravate asthma occurrence. This study aimed to determine the association between short-term lagged PM_2.5 exposure and airway inflammation, lung function, and asthma symptom scores among schoolchildren in communities in the Highveld high-pollution region in South Africa.

Methods: A cross-sectional study was conducted among schoolchildren aged 9-14 years in six communities in the Highveld region in South Africa, between October 2018 and February 2019. A NIOX 200 instrument was used to measure fractional exhaled nitric oxide (FeNO). Lung function indices (forced expiratory volume in one second [FEV₁]; forced vital capacity [FVC] and FEV₁/FVC) were collected using spirometry and the percent of predicted of these was based on the reference equations from the Global Lung Initiative, without ethnic correction. These values were further analyzed as binary outcomes following relevant thresholds (lower limits of normal for lung function and a cutoff of 35 ppb for FeNO). Asthma symptoms were used to create the asthma symptom score. Daily averages of PM_2.5 data for the nearest monitoring station located in each community, were collected from the South African Air Quality Information System and created short-term 5-day lag PM_2.5 concentrations. Additional reported environmental exposures were collected using standardized instruments.

Results: Of the 706 participating schoolchildren, only 1.13% of the participants had doctor-diagnosed asthma, compared to a prevalence of 6.94% with an asthma symptom score suggestive of asthma. Lag 1 (odds ratio [OR]: 1.01; 95% confidence interval [CI]: 1.00, 1.02, P = 0.039) and 5-day average lagged PM_2.5 (OR: 1.02; 95% CI: 0.99, 1.04, P = 0.050) showed increased odds of the FeNO > 35 ppb. Lung function parameters (FEV₁ < lower limit of normal [LLN] [OR: 1.02, 95% CI: 1.00, 1.03, P = 0.018], and FEV₁/FVC < LLN [OR: 1.01; 95% CI: 1.00, 1.02, P < 0.001]) and asthma symptom score ≥ 2 (OR: 1.02; 95% CI: 1.00, 1.04, P = 0.039) also showed significant associations with lag 2, lag 4 and lag 1 of PM_2.5, respectively.

Conclusion: Lagged PM_2.5 exposure was associated with an increased odds of airway inflammation and an increased odds of lung function parameters below the LLN particularly for the later lags, but a significant dose-response relationship across the entire sample was not consistent.