120 AJTCCM VOL. 30 NO. 3 2024
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Background. Exposure to air pollution can cause adverse health eects in people living with chronic lung disease. In people with asthma,
it is not clear whether strategies to reduce outdoor air pollution can aect clinical symptoms and lung function.
Objectives. To determine strategies to reduce air pollution exposure for people with asthma, and to describe the eect of reduced air
pollution on asthma outcome.
Methods. A systematic review was conducted of six databases for English literature. Any study published between April 2012 and March
2022 that mentioned air pollution exposure reduction and asthma was reviewed. Two reviewers (STH and RMp) screened and extracted
the data separately, using a standardised form based on the Cochrane data extraction tool. Risk of bias was assessed using the risk-of-
bias 2 tool. Outcome measures were the Asthma Control Test (ACT), the Childhood Asthma Control Test, exacerbations, and the forced
expiratory volume in the 1st second (FEV1), forced vital capacity (FVC) and FEV1/FVC ratio. e study was registered with PROSPERO
(reg. no. CRD42022341648).
Results. Of the 11 116 identied studies, eight met the inclusion criteria, with a total of 11395043 participants. Clean air policy
implementation modestly improved lung function, as shown by an increase in FVC and FEV1 of 0.02 L/year and 0.01 L/year, respectively.
Reduction of exposure to outdoor smoke pollution with use of mobile application alerts resulted in behavioural change and improved ACT
scores over 8 weeks (mean (standard deviation (SD)) 21.5 (2.3) compared with baseline (20.0 (2.4); p<0.001). Asthma control improved
during low levels of pollution related to COVID-19 lockdown, as shown by mean (SD) ACT scores (17.3 (4.7) v. 19.7 (4.5); p<0.001) and
associated declines in mean daily hospital admissions (4.5 (3.4) days v. 2.8 (2.5) days; p<0.001).
Conclusion. Air pollution is a major hazard, and strategies to reduce exposure have a positive outcome in terms of the asthma morbidity.
is eld would benet from further high-quality randomised clinical trial evidence to inform policy and decision-making.
Keywords. Air quality, pollution, asthma, clean air, policy.
Afr J Thoracic Crit Care Med 2024;30(3):e1992. https://doi.org/10.7196/AJTCCM.2024.v30i3.1992
Idencaon of studies via databases and registers
Asthma is one of the most common chronic diseases in children,
adolescents and adults, leading to considerable morbidity and
mortality worldwide.[1-3] Approximately 300 million people globally,
including ~10% of children, have asthma.[4] Morbidity from asthma is
highest in low- to middle-income countries where air quality is poor.[5]
Previous studies have shown that exposure to outdoor pollutants can
worsen asthma control,[6] and high outdoor pollution levels have been
associated with an increased risk of asthma in childhood.[7] Children
with high early-life air pollution exposures, particularly to trac-
derived pollutants, have an increased risk of a diagnosis of asthma
during the preschool years.[8]
Strategies to reduce air pollution levels include optimising driving
style and vehicle settings, low emission zones, cleaner air fuel sources,
and a more stringent regulatory environment to mitigate outdoor
Interventions to reduce the impact of outdoor air pollution
onasthma: A systematic review
S T Hlophe,1 MB ChB, MMed (Paed), DCH (SA), FC Paed (SA), Cert Critical Care (SA) Paed ;
R Mphahlele,1 MB ChB, Dip Allerg (SA), PhD; K Mortimer,1,2 BA, MA, MB BCh, FRCP, MSc, PhD;
R Masekela,1 MB BCh, MMed (Paed), Dip Allerg (SA), FC Paed (SA), Cert Pulmonology (SA) Paed, PhD
1 Department of Paediatrics and Child Health, School of Clinical Medicine, Nelson R Mandela School of Clincal Medicine, University of KwaZulu-Natal, Durban,
South Africa
2 Cambridge Africa, Department of Pathology, University of Cambridge, UK
Corresponding author: R Masekela (masekelar@ukzn.ac.za)
Study synopsis
What the study adds. e prevalence and burden of asthma are increasing globally. Air pollution exposure is a major cause of worse asthma
symptoms. Strategies to reduce air pollution or exposure to it may contribute towards improved quality of life. is study highlights potential
strategies and their eect on asthma outcome.
Implications of the ndings. A combination of individual activities and actions by governments to reduce air pollution can improve asthma
outcome. A focus on education together with behavioural changes can reduce exposure at the individual level. Implementation of clean air
policies reduces air pollution exposure and improves lung health
AJTCCM VOL. 30 NO. 3 2024 121
ORIGINAL RESEARCH: ARTICLES
pollution from industry and vehicle emissions.[9] At the individual
level, strategies that reduce exposure include use of close-fitting
N95 particulate respirators, face masks, changing of walking/cycling
routes, and air quality alerts and education to reduce trac-related
particulate matter ≤2.5 microns in diameter (PM2.5) exposure.[10-14]
Choosing low-trac routes can decrease exposure of cyclists and
walkers to air pollutants, potentially reducing associated detrimental
health eects.[12] Air quality alerts and education inuence a range of
behaviour change outcomes, including self-ecacy, perception of risk,
action planning and preventive behaviours.[15,16]
We therefore conducted this systematic review to assess which
strategies to reduce outdoor air pollution at an individual or
community level can influence asthma outcomes in children,
adolescents and adults.
Methods
Search strategy
The systematic review protocol was developed and registered
with PROSPERO (reg. no. CRD42022341648). We used the
Population, Intervention, Comparison, Outcomes and Time
(PICOT) framework to aid with the systematic search. e review
is reported in accordance with the Preferred Reporting Items for
Systematic Reviews and Meta-Analyses (PRISMA) guidelines.[17] e
following databases were searched: Clinical Trials Registry Platform
and Cochrane Central Register of Controlled Trials (CENTRAL),
EBSCOHost, PubMed, Science Direct, Scopus and Web of Science.
We also conducted a search on low emission zone articles. Only
scientic articles written in English published between 1 April 2012
and 31 March 2022 were included.
e search strategy was structured to include terms for ‘air pollution’,
‘asthma’, ‘reduction strategy’, ‘reduction methods’, ‘asthma symptoms’,
‘asthma control test’ and ‘lung function test’. e full electronic search
strategy is shown in Supplementary File 1 (available online at https://
www.samedical.org/le/2260).
Selection of studies
Two reviewers (STH and RMp) independently screened articles
identied by searching the electronic databases, using a three-stage
review with initial search by title, followed by the abstract and then
the full text. e full text of potentially eligible studies was evaluated
against the review criteria to identify articles for inclusion. A third
reviewer (RMa) was available at each stage in case of disagreements.
Inclusion and exclusion criteria
Studies were selected in accordance with the eligibility criteria (Table1).
All studies that focused on air pollution reduction interventions and
their impact in people with asthma were included. Control groups were
any in which participants had no air pollution exposure reduction.
Eligible outcomes were improved asthma outcomes including
symptom control as measured by the Asthma Control Test (ACT),[18]
the Childhood Asthma Control Test (c-ACT),[18] asthma exacerbations,
and lung function as measured by the forced expiratory volume in the
1st second (FEV1), the FVC (forced vital capacity) and the ratio of
FEV1 to FVC. We included randomised controlled trials (RCTs) (e.g.
parallel, cluster and crossover trials) and non-randomised studies that
included a comparison treatment arm (i.e. any quantitative study that
investigated the eectiveness of an intervention aimed to assess our
objectives and did not use randomisation to allocate participants to
intervention or comparator groups – e.g. cohort studies or controlled
before-and-aer studies). Studies identied from searching electronic
databases were combined and duplicates were removed. We excluded
any grey literature from experts in the eld, conference abstracts or
unpublished material.
Data extraction and quality assessment
Data on study design, setting, population, authorship and statistical
analysis were extracted from full texts of the included studies using
a standardised form based on the Cochrane data extraction form[19]
(Supplementary File 2, https://www.samedical.org/le/2261). STH
and RMp independently assessed the risk of bias for each study using
the risk-of-bias 2 (RoB 2) tool.[20]
Data analysis and synthesis
Owing to the heterogeneity of study designs, we could not perform a
meta-analysis and summarised the data in a narrative. We therefore
grouped the studies according to intervention and outcome.
Results
ere were 11 116 articles identied through searching electronic
databases (CENTRAL n=3, EBSCOHost n=2 738, PubMed n=4 786,
Science Direct n=2 925, Scopus n=254 and Web of Science n=410). Of
these, 2 852 duplicates were excluded and further 8 131 were excluded
on title review. Aer further abstract screening, 118 were excluded.
e remaining 15 were assessed for eligibility on full article review, of
which 7 were excluded, leaving 8 for inclusion in the review (Fig.1).
Characteristics of the interventions
Eight studies met the inclusion criteria, including two RCTs, with a
total of 11395043 participants (Table2). e ages of participants
ranged from 0 to ≥65 years. Interventions included use of an air
quality alert mobile application, implementation of emission
reduction and adoption of clean air policies, lockdown measures
during the COVID-19 pandemic, and an educational programme.
e outcomes measured were asthma symptoms, ACTs, lung function
tests, admission rates and emergency department (ED) visits.
Air quality alerts
In a population-based cohort study of introduction of an air quality
alert programme in Toronto, Canada, using an online platform,
there was some reduction in asthma symptoms.[21] ere was a strong
eect for the air quality alert programme, with 4.7 fewer asthma-
related ED visits per 1 000 000 people per day (95% condence
interval (CI) 0.55 - 9.38), or in relative terms a reduction of 25%
(95% CI 1 - 47) in ED visits.[21]
e Smoke Sense Urbanova (SSU) smartphone application forecasts
visualisation of quality of air. An intervention with the SSU with
additional alerts to maximise risk reduction on the application SSU
Plus (SSU-P) in Washington State, USA, was studied.[22] In an 8-week
RCT with three study arms, i.e. SSU-P v. SSU and no intervention,
there was a small but statistically signicant increase in ACT scores
at week 8 in the SSU-P arm (mean (standard deviation (SD)) 21.5
(2.3)) compared with baseline (20.0 (2.4); p=0.0008). ere was no
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dierence in the ACT scores comparing the SSU with no intervention
at week 8 (21.0 (4.0)) from baseline (21.3 (2.1)).[22]
For the lung function test, surprisingly there was a decrease in
FEV1 percentage predicted in the SSU-P group at week 8 (mean
(SD) 88.6% (17.2%)) compared with baseline (94.9% (16.2%);
p=0.0172). This decrease was not found in the SSU arm, with a
mean percentage predicted FEV1 at week 8 of 95.6% (17.2%)
compared with baseline (97.6% (14.6%); p>0.05). In the control
arm, there was also no change in mean percentage predicted FEV1
at week 8 (92.9% (16.0%)) compared with baseline (88.4% (20.2%);
p>0.05).[22]
Clean air policy implementation
Adar etal.[23] studied the adoption of clean air technology and fuel
policy compared with the pre-policy period in Washington State,
USA. In this study, a natural experiment to examine associations
between clean air technologies and fuels in school buses and children’s
health was conducted. e adoption of ultra-low-sulphur diesel was
associated with small clinically meaningless increases in lung function,
0.02 (95% CI 0.003 - 0.05) L/yr for FVC and 0.01 (95% CI –0.006 -
0.03) L/yr for FEV1. Although these associations were generally robust
to control for multiple interventions, they had wide CIs and could not
be distinguished from no association.[23]
In Korea, the impact of implementation of air pollution emission
reduction policies was assessed in the capital city, Seoul, and a
metropolitan city, Daejeon.[24] Air pollutant emissions were decreased
during the study period. Total emissions in Seoul were relatively
greater than those in Daejeon. A comparison of the two cities
found an association between emission reductions and reduced
ambient concentrations. Trends in hospital visit rates for asthma,
which had previously been increasing in Seoul, decreased aer the
implementation of the policies. Prevented hospital visit cases for
asthma in Seoul in the total population and the younger population
(0 - 18 years) were estimated as 500 000 (11.3% of hospital visit cases
if there was no intervention) and 320 000 (15.5% of hospital visit cases
if there was no intervention), respectively.[24]
Lockdown
A study in Riyadh, Saudi Arabia, that assessed the impact of the
COVID-19 lockdown period on patients with severe asthma treated
with biologics showed a change in mean (SD) ACT scores from 17.3
(4.7) before the lockdown to 19.7 (4.5) aer 12 weeks of lockdown.[25]
is nding suggested signicant improvement in the control of
asthma, with a mean dierence of 2.4 (3.7) (p<0.001). ere was also
an increase in the proportion of patients who were controlled before
and aer 12 weeks of lockdown (41% v. 60.7%). Levels of carbon
monoxide, sulphur dioxide and nitrogen dioxide were all shown to
decrease in Riyadh region compared with the months before the
lockdown. All these pollutants are directly linked to the trac and
industrial activity in the area.[25]
A study assessing ambient air pollutant concentrations and
asthma-related hospital admissions during COVID-19 transport
restrictions found improvements in air quality in Dublin, Ireland.
During the period of transport restrictions, there was a signicant
decrease in mean daily concentrations of both PM2.5(8.9 v. 7.8 μg/m3;
p=0.002) and nitrogen dioxide(24.0 v. 16.7 μg/m3; p<0.001).[26] ere
was a statistically signicant reduction in average daily admissions for
asthma (mean (SD) 4.5 (3.4) v. 2.8 (2.5); p<0.001). ere was also a
statistically signicant reduction in inpatient median (interquartile
range) bed days (6.0 (2.0 - 14.0) v. 3.5 (0.5-9.0); p<0.001).[26]
Education
In Pennsylvania, USA, an inner-city home-based asthma education
and environmental remediation programme that addressed both
indoor and outdoor triggers through collaboration between a health
system and a local environmental justice organisation showed some
improvement, although not statistically signicant, in pre- and post-
test ACT scores in children with asthma.[27] For the children who began
with a c-ACT or ACT score <20, there was signicant improvement
from pre-test to post-test (c-ACT p<0.001, ACT p=0.050) and a mean
dierence of 3 and 4 points, respectively.
A small RCT in Korea, with 30 participants, assessed dierent modes
of education on asthma control status. Immersive virtual reality (VR)
education involved sitting in front of a computer using an Oculus
Ri DK2 head-mounted display system (Facebook Technologies,
LLC, USA) set to an environmental education programme.[28] e
control group received a verbal explanation from an asthma medical
professional for the same amount of time, together with printed
material used for environ mental management education for asthma
patients in the clinic. e education time was 15 minutes for both
the VR and the control groups. ere was no signicant dierence
between the ACT scores in the two study arms before and aer the
programme (p>0.05).[28]
Risk of bias
Most of the studies reviewed have a high risk of bias as a result of the
study methodology (Table3). ere was no randomisation in six of the
eight studies. In some studies, there was lack of clarity on participant
recruitment, selection and allocation. e outcomes measured could
have been influenced by multiple confounders. A meta-analysis
could not be completed owing to heterogeneity in methodology and
multiple outcomes measured.
Discussion
In this systematic review, we identified multiple interventions to
improve air quality and their outcomes, including the eect on asthma.
Of the eight eligible studies, with a total of 11395043 participants, only
two were RCTs. Interventions included population-level interventions
such as air quality alerts, which showed improvement in asthma
control and ED visits. Use of mobile technology applications with
alerts also resulted in modest improvements in asthma control, but
not in lung function. Additionally, air pollution reduction measures
such a clean air policy improved air quality, but disappointingly did
not meaningfully improve lung function.
Air quality alerts are reported to be more eective when combined
with behavioural changes following high alert notication. e US
Environmental Protection Agency’s Smoke Sense app has been
widely used, but self-selected users responded to symptoms rather
than preventing symptoms via risk reduction.[29] Globally, air quality
alert programmes represent one of the most common public responses
to protect the population from air pollution.[22] However, few studies
have measured the eectiveness of mobile applications on objective
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ORIGINAL RESEARCH: ARTICLES
measures of wildre smoke risk reduction or
asthma-related clinical outcomes.[29,30] The
app myAirCoach demonstrated eectiveness
in improving asthma control but not lung
function at 6 months.[30] Alert announcements
reduced asthma-related ED visits by 25% in
one study, and these air quality assessments
can be done via online services as well.[21,31]
e COVID-19 lockdown was associated
with significantly reduced air pollution
globally. Air pollution emission reduction
policy implementation showed reduced
asthma exacerbations requiring ED visits,
improved asthma control and fewer
asthma-related admissions. Reductions
in transportation sector emissions are
largely responsible for the nitrogen dioxide
anomalies.[32] Pollution in some of the
epicentres of COVID-19, such as Wuhan,
Italy, Spain, the USA and Brazil, decreased by
up to 30%.[33] e lockdown in Yichang was
associated with a decrease in hospital and
outpatient visits for asthma.[34] Many countries
reported that hospitalisations due to asthma
decreased substantially during the pandemic.
It is not clear whether the decreases were due
to a reduction in symptoms, reluctance to
visit hospitals, or reduced exposure to viral
infections. Lockdown with social distancing
measures was the major measure to mitigate
cross-infection and spread of COVID‑19.[35-
37] Benets have also been observed following
local air quality interventions associated with
factory closures. Hospital admissions for
childhood asthma fell by half, in association
with a signicant reduction in PM2.5, as a
result of a 13-month closure of a steel mill in
Utah Valley.[38]
Reduction in air pollution can also be
achieved through adopting clean, efficient
and expanded public transport systems
coupled with car share/club schemes and as
much active transport in the form of walking
and safe cycling as is feasibly possible.[11]
Decreases in ambient nitrogen dioxide and
PM2.5 between 1993 and 2014 in one study
were associated with a deceased asthma
incidence.[39] One of the studies in this review
showed that adoption of ultra-low-sulphur
diesel was associated with improvements in
lung function, but this was not statistically
signicant with wide CIs and could not be
distinguished from no association.[23]
Vehicle electrification has substantial
potential to reduce climate change damage
and air pollution damage.[40] Data from
many parts of the world strongly suggest that
policies designed to reduce air pollution can
improve respiratory outcomes.[11] Deciding
upon and executing the necessary policies
is a complex challenge when it necessitates,
among other measures, a reduction in road
trac and a cleaner and greener element to
what remains on the road – coupled with a
heavy burden of expenditure. Policymakers
are invariably torn between tightening
controls on emissions to enhance health and
succumbing to economic pressures not to
reduce emissions.[11]
The National Asthma Education and
Prevention Program in the USA recommends
that disparate groups receive culturally
competent clinical asthma management
and patient education, and recommends
community-based interventions to include
education and remediation of pollutants
Records identied from
databases (N=11 116)
CENTRAL
EBSCOHost
PubMed
Science Direct
Scopus
Web of Science
ScreeningIncluded Identication
Records removed before screening:
Duplicate records removed,
n=2 852
Title not related to the study,
n=8 131
Abstracts screened,
n=133
Excluded:
Records excluded on abstract review
(not related),
n=118
Studies assessed for eligibility,
n=15
Excluded:
Not related to PICOT on full article
review,
n=7
Studies included in review,
n=8
Fig.1. Study eligibility chart according to Preferred Reporting Items for Systematic Reviews and Meta-
Analyses (PRISMA) criteria. (PICOT = Population, Intervention, Comparator, Outcome, Time.)
Table1. PICOT search criteria
Population
Studies with participants who have asthma and exposure to outdoor
air pollution
Participants of any age, any gender, and any asthma severity
Intervention Any form of outdoor air pollution reduction strategies
Comparator No interventions done to reduce exposure to outdoor air pollution
Outcome e primary outcome measure was asthma outcomes such as symptom
control as measured by the ACT or c-ACT, asthma exacerbations, and
lung function as assessed by FEV1, FVC and ratio of FEV1 to FVC
Time Studies published between April 2012 and March 2022
PICOT = Population, Intervention, Comparator, Outcome, Time; ACT = Asthma Control Test; c-ACT = Childhood Asthma
Control Test; FEV1 = forced expiratory volume in the 1st second; FVC = forced vital capacity.
124 AJTCCM VOL. 30 NO. 3 2024
ORIGINAL RESEARCH: ARTICLES
Table2. Characteristics of interventions
First author
and year Study design Country
Total
participants, NAge (years) Intervention Comparator
Outcome
measured Results
Study period/
follow‑up
Chen,
2018[21]
Regression
discontinuity
study design
Canada,
Toronto
All individuals
who resided
in the city
of Toronto
(Ontario) from
2003 to 2012
2.6 million
All ages Air quality alert
programme
Pre-
programme
Asthma-
related ED
visits
Alert announcements reduced
asthma-related ED visits by
4.7per 1000000 people per day
(95% CI 0.55 - 9.38), or 25%
(95% CI 1 - 47).
One year (143 days fell
within 5 units around
the AQI threshold).
Of these, 41 days were
above the threshold
(AQI ≥48) and
therefore classied
as eligible for alerts
(eligible days).
Postma,
2021[22]
RCT USA,
Washington
State
67
n=22 controls
n=22 SSU
n=23 SSU-P
18 - 26 SSU
SSU-P
No
intervention
ACT and FEV1Increased ACT and decreased
predicted FEV1 from baseline
in the intervention group.
Increased ACT and no dierence
in predicted FEV1 from baseline
in the control group.
8 weeks
Adar,
2015[23]
Cohort USA,
Washington
State
275
n=126 no
asthma
n=126
intermittent
asthma
n=23 persistent
asthma
6 - 12 Adoption of clean
air technology
and fuel
Pre-policy
adoption
AP reduction
and improved
lung health
PM2.5 and FENO levels were
reduced. Changes in FVC and
FEV1 (0.02 (95% CI 0.003 -
0.05) and 0.01 (95% CI –0.006
- 0.03) L/yr, respectively) were
insignicant. Lower absenteeism
(8% reduction (95% CI –16 - –1)
with ULSD.
4 years
Kim,
2019[24]
Cohort Korea, Seoul
and Daejeon
Seoul 8789 984
Daejeon 1466
172
0 - ≥65 Implementation
of AP emission
reduction policies
Population from
metropolitan city
Daejoen
compared
with Seoul
Hospital visits
for asthma
Air pollution
reduction
Prevented hospital visits cases
for asthma in Seoul in the
total population and younger
population (0 - 18 years) were
estimated as 500 000 (11.3%
of hospital visit cases if there
was no intervention) cases
and 320000 (15.5% of hospital
visit cases if there was no
intervention) cases, respectively.
9 years
2003 - 2007 pre-
policies
2008 - 2011 post
implementation
Ayaz,
2021[25]
Cohort Saudi Arabia,
Riyadh
56 22 - 61 Lockdown Pre-
lockdown
Asthma
control
50% reported better symptoms,
38% less use of bronchodilators,
ACT ≥20 improved post
lockdown from 41.1% to 60.7%
(p=0.001). Levels of CO, SO2 and
NO2 were decreased.
12-week lockdown
continued
AJTCCM VOL. 30 NO. 3 2024 125
ORIGINAL RESEARCH: ARTICLES
in the indoor environment and outdoor air.[41] e studies on the
impact of education on asthma control report conicting results.[27,28]
In one study, addition of the Air Quality Index to asthma action
plans led to improved asthma control as shown by ACT scores.[42]
e strength of this systematic review lies in the broad search, which
was also not limited by age or countries’ income status. Limitations
include that a meta-analysis was not possible owing to the small
number of studies and the heterogeneity of studies, and that a funnel
plot to compare the precision and the results of the studies was not
possible. Most studies were at high risk of confounding and bias.
Conclusion
Air pollution is a major hazard, and strategies to reduce exposure have
positive outcomes in terms of the asthma burden. Implementation of
global measures that aim to reduce exposure to air pollutants, such as
air pollution reduction policy implementation, education, air quality
alerts and behavioural change, is recommended to improve asthma
(and wider health) outcomes. We found some evidence that outdoor
air pollution reduction interventions had benecial eects on asthma
control. This field would benefit from further high-quality RCT
evidence to inform policy and decision-making.
Recommendations
A wider range in terms of time frame is recommended to widen the
search pool. We recommend inclusion of both indoor and outdoor air
pollution exposure in the hope of yielding a better result in determining
the burden of air pollution and its impact on asthma. e ndings of
the present review indicate that focusing of education together with
behavioural changes can reduce exposure at the individual level. e
implementation of clean air policies reduces air pollution exposure
and as a result improves lung heath.
Declaration. RMa is a member of the editorial board.
Acknowledgements. We thank Andre Amaral for his review of the
manuscript during its preparation.
Author contributions. STH and RMp reviewed the articles. RMa and KM
supervised, resolved conicts and edited the manuscript.
Funding.None.
Conicts of interest.None.
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2. Ferante G, la Grutta S. e burden of pediatric asthma. Front Pediatr 2018;6:186.
https://doi.org/10.3389/fped.2018.00186
3. Asher I, Bissell K, Chiang CY, etal. Calling time on asthma deaths in tropical regions
– how much longer must people wait for essential medicines? Lancet Respir Med
2019;7(1):13-15. https://doi.org/10.1016/S2213-2600(18)30513-7
4. e Global Asthma Report 2022. Int J Tuberc Lung Dis 2022;26(1):1-104. https://doi.
org/10.5588/ijtld.22.1010
5. Mortimer K, Lesosky M, García-Marcos L, etal. e burden of asthma, hay fever and
eczema in adults in 17 countries: GAN Phase I study. Eur Respir J 2022;60(3):2102865.
https://doi.org/10.1183/13993003.02865-2021
6. Tiotiu AI, Novakova P, Nedeva D, etal. Impact of air pollution on asthma outcomes.
Int J Environ Res Public Health 2020;17(17):6212. https://doi.org/10.3390/
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7. Olaniyan TA, Dalvie MA, Jeebhay MF. Ambient air pollution and childhood asthma:
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Table2. (continued) Characteristics of interventions
First author
and year Study design Country
Total
participants, NAge (years) Intervention Comparator
Outcome
measured Results
Study period/
follow‑up
Kelly,
2022[26]
Cohort Ireland,
Dublin
4 551
admissions
n=3 573 pre
n=978 post
Mean (SD)
40.9 (20.3)
Lockdown Pre-
lockdown
Change in
air pollution
levels and
asthma
admissions
Both PM2.5 and NO2 (p=0.002
and p<0.001, respectively)
were decreased. Daily asthma
admissions (mean (SD))
decreased from 4.5 (3.4) to 2.8
(2.5) (p<0.001).
802 days pre-
pandemic and 353
days during pandemic
Shani,
2015[27]
Pre- and post
test
USA,
Pennsylvania
80 children 2 - 17 Education about
AP triggers
Pre-
intervention
Reduce
exacerbation
and improve
asthma control
Reduction in emergency room
visits, decreases in school
absenteeism and use of rescue
medications.
6 months
Kim,
2022[28]
RCT Korea 30
n=15 in each
group
Mean (SD)
12 (2.6)
Immersive VR
education
Control ACT
c-ACT
No signicant improvement in
ACT scores before and 4 weeks
aer training.
4 weeks
ED = emergency department; CI = condence interval; AQI= Air Quality Index; RCT = randomised controlled trial; Smoke Sense Urbanova smartphone; SSU-P = SSU Plus smartphone; ACT = Asthma Control Test; FEV1 = forced expiratory volume in 1st second;
AP = air pollution; PM2.5 = particulate matter ≤2.5 microns in diameter; FENO = fraction of exhaled nitric oxide; FVC = forced vital capacity; CO = carbon monoxide; SO2 = sulphur dioxide; NO2 = nitrogen dioxide; SD = standard deviation; VR = virtual reality;
c-ACT = Childhood Asthma Control Test.
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Table3. Risk‑of‑bias assessment of air pollution reduction intervention studies in patients with asthma
First author and year Outcome D1 D2 D3 D4 D5 Overall
Kim, 2022[28] Asthma control status ++++++
Ayaz, 2021[25] Asthma control - + + + + -
Postma, 2021[22] ACT and FEV1++++++
Shani, 2015[27] Reduction in exacerbations and
improved asthma control - + + + + -
Kelly, 2022[26] Asthma admissions - + + + + -
Adar, 2015[23] Improved lung health - + + + - -
Chen, 2018[21] Asthma-related emergency visits - - + + - -
Kim, 2019[24] Hospital visits for asthma - + + + + -
D1 = randomisation process; D2 = deviations from intended interventions; D3 = missing outcome data; D4 = measurement of the outcome; D5 = selection of the reported result;
+ = low risk; – = high risk; ACT = Asthma Control Test; FEV1 = forced expiratory volume in 1st second.
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Received 29 February 2024. Accepted 20 June 2024. Published 11 October 2024.
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