High NO2 concentration in winter: a risk factor for ILD patients

A study on the effect of air pollution on the hospitalisation rate in patients with interstitial lung disease revealed that elevated nitrite concentrations were associated with a 50% increased rate of hospital admissions.

“The body of evidence on the effect of air pollution on pulmonary disease is quite large, but if it comes to interstitial lung disease (ILD), knowledge on air pollution is still in its infancy,” Dr Marya Ghazipura (Marron Institute of Urban Management, NY, USA) said [1]. Today, only 12 studies exist on this topic, with most of them focusing on idiopathic pulmonary fibrosis (IPF), all of them in population-dense regions [2]. Even less is known about the effects of air pollution exposure on non-IPF ILDs in populations that are not in major metropolitan regions. “The aim of our study was to quantify the short-term effects of outdoor air pollution on hospitalisations in a population of patients with ILD in the Intermountain West region of the US,” Dr Ghazipura explained. Therefore, a cohort of 1,365 patients with ILD across this region was followed at the University of Utah, with hospitalisation data collected from 2009–2018 [1]. Daily concentrations of major pollutants (atmospheric particulate matter with a diameter of <2.5 micrometres (PM_2.5), nitrite (NO₂), and ozone (O₃)) were calculated using 2 models of exposure assessment: one by ground-level monitors, where weighted concentrations of all monitors within a 20-km radius of the patient were obtained, and one optimal interpolation (OI) model, a validated model integrating satellite remote sensing data.

A time-stratified, case-crossover study was performed using a 14-day interval to estimate the association between short-term exposure to air pollution and hospitalisations. Results were stratified by high (March to October) and low (April to September) ozone months.

There was no association between concentrations of PM_2.5 and O₃ and risk of hospitalisation in both models. In contrast, the OI model found that in the colder season an interquartile increase in daily average NO₂ exposure was associated with 1.5 times the odds of being hospitalised. This association was significantly more pronounced in male patients. “We would not have been able to detect this significant association with NO₂ if we had only relied on the monitors, considering all the monitor gaps in the Intermountain West region. For NO₂ it was critical to use the OI model,” Dr Ghazipura explained. She concluded that more research on this topic will help to give evidence-based guidance regarding air pollution to this already vulnerable patient group.

1. M Ghazipura. Impacts of air pollution in patients with interstitial lung disease. Session TP066. Diffuse parenchymal lung diseases: ILD, sarcoidosis, IPF, LAM. ATS 2021 International conference, 14-19 May.
2. Harai S, et al. Eur Resp Rev 2020;29:200093.

Posted on 17 May, 20214 August, 2021