Asthma is a chronic disease with episodic exacerbations involving inflammation of the bronchial airways, which results in symptoms such as shortness of breath, coughing, wheezing or exercise intolerance [1]. Childhood asthma is a common, and often serious, chronic disease in infants and children. The prevalence of childhood asthma is increasing among low-and middle-income countries [2]. ISAAC (International Study of Asthma and Allergies in Children) conducted surveys in 97 countries between 2000 and 2003 and found that about 14% of the world's children were likely to have asthmatic symptoms [3]. Recent studies on childhood asthma conducted across India have shown its prevalence to be ranging from 7.9% to 13.1% in school-going children [4, 5]. A study conducted in Bangalore by Paramesh, who studied 20,000 children under the age of 18 years, has shown that the prevalence of asthma has increased over threefold over two decades, from 9% in 1979 to 29.5% in the year 1999 [6]. It has been reported in the United States that asthma among school-going children was responsible for 7 million missed school days and an annual cost of $211 million. [7].
Several risk factors are known to be associated with asthma, both intrinsic or extrinsic, which result in the varying severity of asthma. These include familial history, birth weight, breastfeeding, environment, exercise, furry pet ownership, smoking habits among family members, absence of smoke outlet in the house, and other allergies like dermatitis and/or rhinitis [8,9,10,11].
There is a dearth of studies that focus on risk factors for childhood asthma in the Indian subcontinent. Our study aims to identify the determinants of childhood asthma. The results of this study will help to generate evidence to develop and design targeted interventions to raise awareness to prevent or control these risk factors.
A total of 60 children were included in our study. 30 were cases with childhood asthma and 30 were age- and gender-matched controls. Among the study subjects, 55% were under the age of five, 60% were male, and 51% belonged to the upper or upper-middle socioeconomic group. The sociodemographic details of the study sample are described in Table 1.
Sociodemographic factors in childhood asthma N=60.
Age | Under 5 | 17 (56.7) | 16 (53.3) | 1.14 (0.41–3.16) | 0.79 |
Above 5yrs | 13 (43.3) | 14 (46.7) | |||
Gender | Male | 18 (60.0) | 18 (60.0) | 1.00 (0.36–2.81) | 0.99 |
Female | 12 (40.0) | 12 (40.0) | |||
Maternal education | Up to High school | 20 (66.7) | 25 (83.3) | 0.4 (0.19–1.36) | 0.14 |
Graduate/Postgraduate | 10 (33.3) | 5 (16.7) | |||
Socioeconomic status | Upper/upper-middle | 18 (60.0) | 13 (43.3) | 1.96 (0.70–5.48) | 0.19 |
Middle/Lower-middle/lower | 12 (40.0) | 17 (56.7) |
Over 61.7% of the participants were firstborn children. Most of the subjects (80%) were born full term (more than 37 completed weeks of gestation), 70% were born via vaginal delivery, and 30% had a birth weight less than 2500g. Around a quarter (23.3%) of the parents of children had a history of allergy/atopy. Risk factors during the antenatal period and birth are depicted in Table 2.
Pre-natal, genetic and birth factors in childhood asthma N=60.
Parity index of mother | Primipara | 9 (30.0) | 9 (30.0) | 1.0 (0.33–3.01) | 0.99 |
Multipara | 21 (70.0) | 21 (70.0) | |||
Birth order | 1 | 16 (53.3) | 21 (70.0) | 0.49 (0.17–1.41) | 0.18 |
≥2 | 14 (46.7) | 9 (30.0) | |||
Parental history of allergy / atopy | Yes | 14 (46.7) | 0 (0) | 3.98 (1.10–6.86) | |
No | 16 (53.3) | 30 (100) | |||
Gestational age at birth | Preterm | 5 (16.7) | 7 (23.3) | 0.66 (0.18–2.36) | 0.52 |
Full term | 25 (83.3) | 23 (76.7) | |||
Mode of delivery | Vaginal (normal/assisted) | 19 (63.3) | 23 (76.7) | 0.53 (0.17–1.62) | 0.26 |
Caesarean section | 11 (36.7) | 7 (23.3) | |||
Birth weight | < 2500 g | 4 (13.3) | 8 (26.7) | 0.42 (0.11–1.59) | 0.17 |
≥ 2500 g | 26 (86.7) | 22 (73.3) |
Penalized odd ratio (Firthlogit regression) to account for 0 value in one of the cells.
Two-thirds (68.3%) of the children were exclusively breastfed for 6 months, whereas pre-lacteal feeds were given to 40.0% of the children. It was found that 5% of the children were underweight and 18% were overweight. One fourth (25.0%) experienced respiratory problems in the neonatal period and 28.3% were admitted to the neonatal intensive care unit [NICU]. Around 60% experienced illness in the first year of life, 41.7% had a history of allergic rhinitis, and 10.0% had a history of skin allergy. More than two-thirds (70.0%) had normal nutritional status. Risk factors in the neonatal period, infancy, and childhood are depicted in Table 3.
Risk factors for childhood asthma in neonatal period, infancy and childhood N=60.
Received pre-lacteal feeds | Yes | 13 (43.3) | 11 (36.7) | 1.32 (0.47–3.72) | 0.60 |
No | 17 (56.7) | 19 (63.3) | |||
Exclusive breastfeeding for 6 months | Yes | 17 (56.7) | 24 (80.0) | 0.33 (0.1–1.03) | 0.052 |
No | 13 (43.3) | 6 (20.0) | |||
Experienced respiratory problems in the neonatal period | Yes | 12 (40.0) | 3 (10.0) | 6.00 (1.48–24.3) | |
No | 18 (60.0) | 27 (90.0) | |||
NICU admission | Yes | 11(36.7) | 6 (20.0) | 2.32 (0.72–7.41) | 0.15 |
No | 19(63.3) | 24 (80.0) | |||
Any illness in the first year | Yes | 24 (80.0) | 12 (40.0) | 6.00 (1.89–19.04) | |
No | 6 (20.0) | 18 (60.0) | |||
Child experiences symptoms of allergic rhinitis | Yes | 23(76.7) | 2 (6.7) | 46 (8.7–243.25) | |
No | 7 (23.3) | 28 (93.3) | |||
History of atopy/allergy | Yes | 6 (20.0) | 0 (0) | 2.78 (0.14–5.71) | |
No | 24 (80.0) | 30 (100) | |||
Nutritional status (present) | Overweight | 5 (16.7) | 9 (30.0) | - | - |
Normal | 22 (73.3) | 20 (66.7) | 0.33 (0.03–3.21) | 0.34 | |
Underweight | 3 (10.0) | 2 (3.3) | 0.91 (0.49–1.67) | 0.76 |
Penalized odd ratio (Firthlogit regression) to account for 0 value in one of the cell.
The majority (61.7%) of the study participants lived in an urban area, 23.3% lived in an industrial area, and 38.3% lived in a house near the main road. Nearly half (46.7%) of the houses were overcrowded. The proportion of children exposed to smoke, firewood, incense, and mosquito repellents at home were 18.3%, 15.0%, 40.0% and 38.3% respectively. Around half (43.3%) of the children played with soft toys. Pets were present in 31.7% of households. Around one third (35.0%) had heavy carpets/curtains at home. Risk factors for childhood asthma in the environment and within the house are depicted in Table 4.
Environment and housing factors in childhood asthma N=60.
Residence | Rural | 12 (40.0) | 19 (63.3) | 0.87 (0.31–2.46) | 0.79 |
Urban | 18 (60.0) | 11 (36.7) | |||
Located in industrial area | Yes | 13 (13.3) | 1 (3.3) | 22.18 (2.66–184.79) | |
No | 17 (86.7) | 29 (96.7) | |||
Location of house | Main road | 15 (50.0) | 8 (26.7) | 2.75 (0.93–8.1) | 0.06 |
Away from main road | 15 (50.0) | 22 (73.3) | |||
Overcrowding | Yes | 16 (53.3) | 12 (40.0) | 1.71 (0.62–4.77) | 0.30 |
No | 14 (46.7) | 18 (60.0) | |||
Exposure to tobacco smoke | Yes | 6 (20.0) | 5 (16.7) | 1.25 (0.34–4.64) | 0.74 |
No | 24 (80.0) | 25 (83.3) | |||
Exposure to firewood | Yes | 3 (10.0) | 6 (20.0) | 0.44 (0.1–1.97) | 0.28 |
No | 27 (90.0) | 24 (80.0) | |||
Exposure to incense | Yes | 17 (56.7) | 7 (23.3) | 4.3 (1.41–13.07) | |
No | 13 (43.3) | 23 (76.7) | |||
Exposure to mosquito repellants | Yes | 15 (50.0) | 8 (26.7) | 2.75 (0.93–8.1) | 0.06 |
No | 15 (50.0) | 22 (73.3) | |||
Kerosene for cooking | Yes | 6 (20.0) | 7 (23.3) | 0.82 (0.24–2.81) | 0.75 |
No | 24 (80.0) | 23 (76.7) | |||
Pets in the house | Yes | 12 (40.0) | 7 (23.3) | 2.19 (0.72–6.7) | 0.17 |
No | 18 (60.0) | 23 (76.7) | |||
Synthetic material of child's pillow cover | Yes | 4 (13.3) | 8 (26.7) | 0.42 (0.11–1.6) | 0.2 |
No | 26 (86.7) | 22 (73.3) | |||
Regular washing child's bedlinen | Yes | 27 (90.0) | 24 (80.0) | 2.25 (0.51–9.99) | 0.28 |
No | 3 (10.0) | 6 (20.0) | |||
Child plays with soft toys | Yes | 15 (50.0) | 11 (36.7) | 1.73 (0.62–4.84) | 0.32 |
No | 15 (50.0) | 19 (63.3) | |||
Cockroach infestation at home | Yes | 22 (73.3) | 17 (56.7) | 2.1 (0.71–6.22) | 0.18 |
No | 8 (26.7) | 13 (43.3) | |||
Heavy carpet/curtain/rugs at home | Yes | 15 (50) | 6 (20) | 4.00 (1.27–12.58) | |
No | 15 (50) | 24 (80) |
Significantly higher odds of developing childhood asthma were found in children with parental history of allergy/atopy [OR=2.88 (1.94–4.27),
Multivariate logistic regression analysis was performed on a model which included all risk factors for childhood asthma that showed a significant odds ratio on bivariate analysis. None of the risk factors showed a significant association with childhood asthma in this model. Sub-group multiple logistic regression analysis with all environmental risk factors, adjusted for parental history of allergy, showed that children with houses located in industrial areas [AOR=2.72 (2.6–323.1),
Primary prevention of chronic disease involves the elimination or modification of risk factors for that disease [14]. In our study, we found that the risk factors for childhood asthma were having homes located in industrial areas, history of burning incense at home, parental history of allergy, and history of allergic rhinitis in the child.
In a cohort of 5654 children in Sweden, parental asthma, small-for-gestational age, and male gender were linked to childhood asthma [15]. The Nutrition Evidence Systematic Review team in the USA has published their finding based on a review of 44 studies, which shows that ever breastfeeding is protective against asthma, and that longer duration and exclusivity of breastfeeding offers even greater protection [16]. Determinants found in other studies include male gender, urban locality, low socioeconomic status, damp environment, use of firewood for cooking, presence of pets, family history of asthma/atopy, preterm birth, high body mass index, presence of a smoker at home, and lack of exclusive breastfeeding [17, 18]. A United States National Survey, which included 90,721 children, observed that preterm birth was associated with an increased risk of pre-school wheezing and school-age asthma, independent of birth weight [19]. In our study, except the for parental history of allergy, none of the above determinants were significantly associated with childhood asthma. Asthma and other allergic conditions show familial aggregation. This is due to a complex interplay of hereditary and environmental causes. A multicentric study among children from seven cities in China revealed that the odds of childhood asthma increased 16-fold among children with two asthmatic parents. This study also found that having even one grandparent with asthma doubled the risk of childhood asthma, reinforcing the significance of family history. [20] In addition, exposure to common environmental risk factors among parents and children due to shared living conditions also contributes to familial aggregation of asthma [21].
Our findings show that incense burning and location of house in an industrial area were associated with childhood asthma. A study in China also reported a significant association between incense burning and traffic-related air pollution [22]. Incense burning emits a complex mixture of particulate matter, gases, volatile organic compounds, heavy metals, and other gaseous compounds.
When inhaled, these substances elevate the oxidative stress, impair the lung defences, and lead to declined lung function [23]. The results of our study showed that children with allergic rhinitis had higher odds of developing childhood asthma. Both these conditions demonstrate similar responses at the cellular level and trigger the inflammatory cascade. They differ only in the location of the eosinophil infiltration, depending on whether it is the nasal or bronchial epithelium [24]. Health education should be given to mothers of children with allergic rhinitis regarding reducing exposure to triggers of asthma, including incense.
This hospital-based case control study among children aged two to less than 18 years studied an exhaustive list of possible risk factors. The findings from our study can be used to generate awareness regarding risk factors that are linked to childhood asthma. In clinical practice, the presence of these factors can raise the index of suspicion of childhood asthma. The findings of our study also have policy implications. Municipal authorities should consider approving locations of residential areas away from industrial zones. Children with parental history of allergy and atopy need to be monitored to diagnose childhood asthma early. More research is needed to explore the role of environmental risk factors in childhood asthma in developing countries.
Our study found that homes located in industrial areas, burning incense at home, parental history of allergy, and history of allergic rhinitis in the child are determinants of childhood asthma. The findings from our study can be used to generate awareness regarding risk factors that are linked to childhood asthma.
The study identifies determinants of childhood asthma in an Indian setting: homes located in industrial areas, history of burning incense at home, parental history of allergy, and history of allergic rhinitis in the child.