Short-Term Nitrogen Dioxide Exposure and Emergency Hospital Admissions for Asthma in Children: A Case-Crossover Analysis in England

Abstract

Background

There is an increasing body of evidence associating short-term ambient nitrogen dioxide (NO₂) exposure with asthma-related hospital admissions in children. However, most studies have relied on temporally resolved exposure information, potentially ignoring the spatial variability of NO₂. We aimed to investigate how daily NO₂ estimates from a highly resolved spatio-temporal model are associated with the risk of emergency hospital admission for asthma in children in England.

Methods

We conducted a time-stratified case-crossover study including 111,766 emergency hospital admissions for asthma in children (aged 0–14 years) between 1st January 2011 and 31st December 2015 in England. Daily NO₂ levels were predicted at the patients’ place of residence using spatio-temporal models by combining land use data and chemical transport model estimates. Conditional logistic regression models were used to obtain the odds ratios (OR) and confidence intervals (CI) after adjusting for temperature, relative humidity, bank holidays, and influenza rates. The effect modifications by age, sex, season, area-level income deprivation, and region were explored in stratified analyses.

Results

For each 10 µg/m³ increase in NO₂ exposure, we observed an 8% increase in asthma-related emergency admissions using a five-day moving NO₂ average (mean lag 0–4) (OR 1.08, 95% CI 1.06–1.10). In the stratified analysis, we found larger effect sizes for male (OR 1.10, 95% CI 1.07–1.12) and during the cold season (OR 1.10, 95% CI 1.08–1.12). The effect estimates varied slightly by age group, area-level income deprivation, and region.

Significance

Short-term exposure to NO₂ was significantly associated with an increased risk of asthma emergency admissions among children in England. Future guidance and policies need to consider reflecting certain proven modifications, such as using season-specific countermeasures for air pollution control, to protect the at-risk population.

Keywords:

• asthma
• nitrogen dioxide
• children
• hospital admissions
• case-crossover

Data Sharing Statement

Data may be obtained from a third party and are not publicly available. The UK Small Area Health Statistics Unit (SAHSU) does not have permission to supply data to third parties.

Acknowledgment

We thank Hima Daby, Gajanan Natu, and Eric Johnson for their assistance with the data acquisition, storage, preparation, and governance. The views expressed are those of the authors. This paper does not necessarily reflect the views of the National Institute for Health and Care Research or the Department of Health and Social Care. Hospital Episode Statistics (hospital admissions) data are copyright © 2023, re-used with the permission of NHS Digital. All rights reserved.

The abstract of this paper was presented at the 34th Annual Conference of the International Society for Environmental Epidemiology as a poster presentation with interim findings. The poster’s abstract was published in “ISEE Conference Abstracts”: https://doi.org/10.1289/isee.2022.P-0424.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

The work of the UK Small Area Health Statistics Unit (SAHSU) is overseen by the UK Health Security Agency (UK HSA). SAHSU is part of the MRC Centre for Environment and Health supported by the UK Medical Research Council (MR/S019669/1, 2019–2024), and the National Institute for Health and Care Research (NIHR) through its Health Protection Research Units (HPRU) at Imperial College London in Environmental Exposures and Chemical Radiation Threats and Hazards, and through Health Data Research UK (HDR UK). Infrastructure support for the Department of Epidemiology and Biostatistics was provided by the NIHR Imperial BRC.