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 Table of Contents  
Year : 2020  |  Volume : 64  |  Issue : 2  |  Page : 124-129  

Air pollution and weather as the determinants of acute attacks of asthma: Spatiotemporal approach

1 Director Professor, University College of Medical Sciences, University of Delhi, Delhi, India
2 Insurance Medical Officer, ESI Dispensary, Dwarka, Delhi, India
3 Consultant, Sleep and Critical Care Medicine, Primus Super Specialty Hospital, Delhi, India
4 Associate Professor, Department of Environmental Studies, University of Delhi, Delhi, India
5 Research Associate, Center for Atmospheric Sciences, Indian Institute of Technology, Delhi, India

Date of Submission19-Mar-2019
Date of Decision29-May-2019
Date of Acceptance15-Apr-2020
Date of Web Publication16-Jun-2020

Correspondence Address:
Arun Kumar Sharma
Director Professor, University College of Medical Sciences, Dilshad Garden, Delhi - 110 095
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijph.IJPH_135_19

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Background: Although air pollution and weather changes have been identified as putative risk factors that precipitate acute attacks of bronchial asthma, so far there have been no studies that could conclusively establisha clear association. Objectives: This study was carried out to investigate the effect of the concentrations of NO2, SO2, and particulate matter on exacerbation of bronchial asthma. Methods: A longitudinal study was conducted during February 2014–January 2015. Sixty-one known cases of asthma were recruited from the outpatient department of a chest hospital. Data regarding weather parameter (temperature, rainfall, and relative humidity) and environmental pollution (SO2and NO2) and respirable suspended particulate matter were procured from the Indian Meteorological Department and Delhi Pollution Control Committee, respectively. Association was examined using the generalized estimation equation (GEE). Results: Separate models were developed for weather parameter and pollution parameters. This study could not find a significant association between any of the weather parameters and occurrence of asthmatic attacks. In the GEE model, where average values of SO2, NO2, and PM were used, the PM was found to be significantly associated with asthmatic attacks. Conclusion: PM was found to increase the risk of exacerbation of asthma three folds.

Keywords: Air pollution, asthma exacerbation, cohort study, Global Positioning System, weather

How to cite this article:
Sharma AK, Saini S, Chhabra P, Chhabra SK, Ghosh C, Baliyan P. Air pollution and weather as the determinants of acute attacks of asthma: Spatiotemporal approach. Indian J Public Health 2020;64:124-9

How to cite this URL:
Sharma AK, Saini S, Chhabra P, Chhabra SK, Ghosh C, Baliyan P. Air pollution and weather as the determinants of acute attacks of asthma: Spatiotemporal approach. Indian J Public Health [serial online] 2020 [cited 2021 Sep 24];64:124-9. Available from:

   Introduction Top

Since Rio protocol,[1] the effect of pollution and climatic change on human health has gained attention among scientists globally. Although it adversely affects all human organ systems, the respiratory system is most likely to be affected. Burden of respiratory diseases is increased with industrialization and urbanization. Both these phenomena are associated with deterioration in air quality and associated changes in the climate.[2],[3],[4]

Asthma is a major public health problem with over 300 million people being diagnosed every year, and it accounts for 250,000 deaths worldwide annually.[5] As a disease, asthma is a burden for patients, their families as well as the society. It manifests as the restriction of physical activities, with progressive worsening of activity index.

Genetic predisposition and exposure to inhaled particles provoke allergic reactions that lead to the development of asthma. Various researchers have documented evidence about a risk association between some of the air pollutants and changes in the weather parameters with precipitation of acute asthmatic attacks.[6],[7],[8],[9] However, conclusive evidences in this regard are yet to available; these factors failed to establish a consistent and verifiable relationship.[10],[11],[12] Most of the studies investigating the relationship between air pollution, weather changes, and asthma exacerbations are either hospital based or ecological and thus carry very limited value in terms of evidence of relationship. To fill this knowledge gap, we conducted this study to examine the impact of weather changes and air quality on exacerbation of asthmatic attacks.

   Materials and Methods Top

Study design, settings, and subjects

This study with a longitudinal design was conducted during February 2014–January 2015. The study patients were recruited from the outpatient department (OPD) of a chest specialty institute in Delhi by one of the coinvestigators. Due to time constraints, duration of recruitment of patients was restricted to 2 months. Newly diagnosed, confirmed cases of bronchial asthma, over 18 years of age, residing in a radius of 8 km from the institute, were eligible for the inclusion in the study. On fixed OPD days of the coinvestigator, all patients found eligible were included in the study. Over a period of 2 months, 61 cases were recruited.

Data collection: Tools and techniques

After recruitment, each patient was visited at his/her home. Informed consent was obtained before data collection from each individual. A patient information sheet was provided to all participants during the first visit itself. Information was collected regarding the sociodemographic profile using a structured, pilot-tested interview schedule. The household was surveyed and details regarding the presence of known risk factors for bronchial asthma were recorded using a detailed check list. Location of kitchen (within living room or a separate kitchen), status of ventilation (adequate/inadequate), potential for exposure to dust, mites, fomites, and aerosols were assessed. Geocoordinates of each household were recorded using a Global Positioning System device. Subsequently, each patient was contacted once in a fortnight personally or telephonically to inquire about any episode of acute exacerbation of asthma in the immediately preceding 15 days. The data collection period was from February 2014 to January 2015. Data regarding weather parameters such as minimum and maximum atmospheric temperature, precipitation, and relative humidity were obtained from the India Meteorological Department (Government of India) on a day-to-day basis. Data on indicators of air pollution, namely sulfur oxides (SO2), nitrogen oxides (NO2) gases, and respirable suspended particulate matter (RSPM) were obtained from the Delhi Pollution Control Committee's air quality monitoring station located at Civil Lines. This monitoring station is also located in a radius of 8 km from the chest institute. From the weather and pollution monitoring data, fortnightly averages were calculated to align with data collection interval for the primary outcome event that is the episode of asthma. Episode of asthma was defined as the occurrence of breathlessness, coughing, tightness in chest, and wheeze.

This study was approved by the Institutional Ethics Committee-Human Research (IEC-HR) of all three participating institutions. Approval by the IEC-HR of University College of Medical Sciences was given by the committee vide letter bearing no. NIL dated 27 November 2013.

Sample size

As the objective of this study was to find the association of number of episodes of acute asthma in known cases of bronchial asthma, with the weather and ail pollution parameters, using generalized estimation equation (GEE); panel data sheet was prepared. Since there were no prior studies available in Delhi or similar geographical regions, a priori sample size was not calculated, nor any hypothesis was developed and the study was considered a pilot study. Due to time bound nature of the study, period of recruitment was restricted to 2 months. During the stipulated time period of 2 months, 61 newly diagnosed cases could be recruited and 61 × 26 = 1586 observations were possible in a calendar year, which was sufficient number of observations for GEE modeling with six independent variables, three each on air pollution (Sox, NOx and RSPM) and weather (temperature, relative humidity, and rainfall).

Statistical analysis

The data were analyzed using Intercooled Stata V9.0© for Windows, and ArcGIS v10.2 (A. StataCorp. 2005. Stata Statistical Software: Release 9. College Station, TX: StataCorp LP. B. ESRI 2011. ArcGIS Desktop: Release 10. Redlands, CA: Environmental Systems Research Institute). The entire dataset was converted into time series data. GEE was used to find the association of episodes of asthma with weather and air pollution variables. Separate GEE models were developed for weather and pollution parameters. Logistic regression analysis was carried out to see if there was any association between the occurrence of episodes of asthma and other known risk factors. Level of significance was set at 5%.

   Results Top

Socio-demographic profile

Sixty-one participants had a mean age of 36.40 years; with 33 (54.1), 20 (32.8) and 08 (13.1) belonging to ≤35, 35–49, and ≥50 years, respectively. Twenty-five (41%) patients were male. About one-third of them (22, 36.1%)

were residing in designated rural areas of Delhi and only 4 (6.5%) were illiterates. By occupation, most of them were homemakers (26; 42.6%), and the rest being semiskilled worker (15; 24.6%), retired/unemployed (10; 16.4%), skilled worker (6; 9.8%), and only 4 (6.6%) being professional worker.

The total number of person-fortnights in a year was 61 × 26 = 1586. However, actual observations were 1250 person-fortnights because 336 person-fortnights were lost to follow-up due to death of 1 participant and migration of 10 participants during the data collection period.

Spatiotemporal variation of asthma exacerbation episodes

During the study period, we observed 60 episodes, thus the overall incidence rate was 4.75/100 person-fortnights. The overall frequency distribution of acute episodes of bronchial asthma is shown in [Figure 1].
Figure 1: Map showing frequency distribution of asthma episodes.

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The temporal distribution of episodes showed that majority of episodes occurred in the quarter of November 14–January 15; covering larger geographical areas, in winter months. In these months, those localities which were free of any episodes during the rest of the year showed the occurrence of new episodes [Figure 2].
Figure 2: (a and b) Temporal distribution of asthma exacerbation episode (quarter-wise).

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The clustering of episodes of asthma was analyzed using Getis Ord Local G statistic. The statistically significant clustering of episodes was noted at two sites which were resettlement colonies, inhabited by families belonging to low socioeconomic status, surrounded by industrial zones and fallow lands [Figure 3].
Figure 3: Clustering of asthma exacerbation episode.

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GEE was used to find the association between weather parameters and frequency of asthma episodes. In this study, we did not find a significant association between other weather parameters such as temperature, rainfall and relative humidity, and occurrence of asthma attacks [Table 1]. Temporal distribution of asthma episodes seemingly showed an association between cold weather and asthma exacerbation, nevertheless, this study failed to observe a statistically significant relationship (P < 0.804).
Table 1: Generalized estimation equation results for association of weather parameters and air pollutant parameters with episodes of acute attacks of asthma

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GEE was also used to find the association between pollution indicators, namely SO2, NO2 and PM with the frequency of asthma episodes. Data were available for daily minimum, maximum and average values. In the GEE model where average values of SO2, NO2, and RSPM were used, the PM was found to be significantly associated with asthmatic attacks (P = 0.031) [Table 1].

   Discussion Top

Seasonal variation of asthma exacerbation

Majority of asthma exacerbation episode in the study cohort were noted in a span of 3 months of winter season (39/37 episodes) in comparison to 24 exacerbation episodes spanned in remaining 9 months. The spatial distribution of all episodes suggests that there are certain areas where the concentration of episodes was more compared to other areas. Patients with no episode in 1 year period were distributed throughout the study area. This could be because of proper guidance and instructions given to them by the treating physician were followed meticulously by them. In our study, the PM was found to be significantly associated with asthmatic attacks. However, the regression coefficient was very small. High-RSPM concentration was noted during winter season, though the difference was not statistically significant, it can be a possible reason for the high number of episodes in the winter season. Stability of air stratification[13] makes dispersion and diffusion of RSPM difficult during winter and raises their concentration in lower atmosphere. In addition, bronchoconstriction, airway congestion, secretion, and decrease in mucocilliary clearance compromise pulmonary mechanics and decrease protection against air pollutants.[14]

Incidentally, cohort studies have been conducted in Australia and USA among children. These studies have reported a positive correlation between the incidence of acute-severe exacerbation of asthma and fluctuations in the PM levels in Australia[15] and with NO2 levels in children in USA.[16] There are ample ecological studies reporting a significant relationship between air pollutants and asthma exacerbations, but they fail to establish a consistent relationship between any one pollutant and asthma exacerbation, for example, with NO2 in Canada,[12] in Sweden,[17] SO2 in Portland,[18] and PM and NO2 in California.[19] An ecological study in Tokyo by Abe et al.,[20] however, reported no association at all.

Our study tried to determine the relationship between ambient weather changes and the reported incidents of acute-severe exacerbation of asthma using correlation statistic. Generalized estimated equation generated by a model to fit fluctuations in the ambient weather patterns and reported the incidences of acute severe exacerbation of asthma failed to prove a significant relationship between the two. Similar results are reported by De Diego Damiá et al.[21] in Spain, Rosas et al.[22] in Mexico, Villeneuve et al.[8] in Canada, and Wasilevich et al.[23] in Michigan.

The robust study design (“cohort”) in itself was the most significant strength of the study. Each patient was followed up for 1 year, thereby generating the data for individual patients which made the study more robust. Other researchers have used “admissions to emergency room” as an outcome measure of acute exacerbation of asthma.[24] Most of the cases reporting in the emergency room with acute severe exacerbation of asthma are unarguably either poorly controlled or uncontrolled. The findings of these subgroups have further been extrapolated to the entire cohort, thereby affecting the validity of such studies. However, in view of differences in the air pollution matrix, the outcome variable and statistical methods were used for the various studies, it is difficult to compare the result of our study with the studies being cited.

Owing to the close monitoring and follow-up of each patient, the present study also included those instances of asthma exacerbations which had not warranted a visit to the emergency room. Being a community-based cohort study, patients were followed up with respect to their exposure to various hitherto understudied potential risk factors such as indoor tobacco smoke exposure, overcrowding, poor ventilation, the absence of a separate cooking space, and presence of pets.

Regular monitoring in this study might have increased awareness in study participants and prompted better compliance with the advised treatment and control guidelines being provided to them from time to time. The increased awareness and better compliance might have led to better control of asthma in study participants even on exposure to air pollutants and weather variables.

In this context, the effect of various factors on the precipitation of acute asthma attacks merit attention, such that the public policy could be designed keeping in mind the needs of these patients, and the devastating effect each attack has on their quality of life, as well as on their economic productivity.


The participants may have been able to take preventive medications in anticipation of any potential exposure to one or more trigger, thereby reducing the chances of acute exacerbation. A loss to follow-up of 16% occurred in the study. These patients might be those whose control over asthma did not improve with the treatment at the associated hospital and may have moved on to other health care providers.

The use of data from fixed sight ambient air pollution monitoring stations in the study may not adequately characterize the actual personal exposure to ambient air pollutants especially since people spend a large proportion of their time indoors where the air pollutant concentrations are lower than the ambient concentration, and also, participants were advised to avoid exposure to known or potential confounders and effect modifiers by the investigators at regular intervals. It may have been difficult for the participants to uniformly follow the advice being given for studies conducted for longer durations like in this study.

The study suffered from the problem of a small output observation, which may have led to the obfuscation of some findings, as smaller the signal in time series study, more difficult it is to isolate it from the noise.

   Conclusion Top

The current study revealed that levels of RSPM were significantly associated with asthma attacks. Close follow-up and regular monitoring of patients in this study may have increased the awareness in study participants and prompted better compliance with the advised treatment and control guidelines being provided to them from time to time. This might have led to better control of asthma in study participants even on exposure to air pollutants and weather variables. Bigger studies with larger output observation and local ambient air-quality metrics are needed to identify the associations between the putative factors and asthma exacerbations.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1]


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