The effects of ambient NO2 and PM2.5 exposure on asthma-related outcomes in school children residing in informal settlements in South Africa.

Abstract

OPS 52: Air pollution and respiratory health, Room 110, Floor 1, August 28, 2019, 10:30 AM - 12:00 PM Background/Aim: No previous epidemiological study has investigated the independent effect of long-term ambient nitrogen dioxide (NO2) and particulate matter smaller than 2.5 µm in diameter (PM2.5) exposure on asthma-related outcomes among school children in Africa. This study aimed to investigate these effects in a cohort of school children in the Western Cape Province of South Africa. Methods: Grade-4 school children (n = 522) residing in four informal settlements were followed for a 12-months period. Spirometry and fractional exhaled nitric-oxide (FeNO) measurements were conducted on each child in addition to the International Study on Asthma and Allergy in Children (ISAAC) questionnaire that was administered to the parent/caregiver at baseline and follow-up. Annual NO2 and PM2.5 levels were estimated for each child’s home using land-use regression modelling. Two-pollutant models were constructed to assess the independent effects of both ambient NO2 and PM2.5 on incident asthma-associated outcomes adjusting-for host characteristics, indoor exposures and residential area. Results: The annual average concentration of PM2.5 and NO2 in the four study areas (10.01 μg/m3 and 16.62 µg/m3 respectively), were below the South Africa National Ambient Air Quality Standards (20 μg/m3 and 40 µg/m3, respectively) for both pollutants. An interquartile range (IQR) increase of 14.2 µg/m3 in NO2 was associated with an increased risk of new onset ocular-nasal symptoms (adjusted odds ratio [aOR]: 1.63, 95% Confidence Interval [CI]: 1.01 – 2.60), wheezing (aOR: 3.57, 95% CI: 1.18 – 10.92), symptom score ≥2 (aOR: 1.71, 95% CI: 1.02 – 2.86), and allergic airway inflammation defined as FeNO > 35 ppb (aOR: 3.10, 95% CI: 1.10 – 8.71), independent of PM2.5 exposures. Conclusion: This study provides evidence of an effect of ambient NO2 below national and international guidelines, independent of PM2.5 exposure, on 12-months incidence of asthma-related outcomes among children residing in informal settlements of South Africa.