|Year : 2020 | Volume
| Issue : 2 | Page : 74-80
Clinical profile and environmental risk factors of asthma in children at a tertiary care teaching hospital in the sub-Himalayan belt of Northern India
Neha Rehalia, Jyoti Sharma, Sanjeev Chaudhary
Department of Pediatrics, Dr. Rajendra Prasad Government Medical College, Kangra, Himachal Pradesh, India
|Date of Submission||01-Feb-2020|
|Date of Acceptance||16-Jun-2020|
|Date of Web Publication||20-Nov-2020|
Dr. Jyoti Sharma
Associate professor. Department of Pediatrics, Dr. Rajendra Prasad Government Medical College, Tanda, Kangra - 176 001, Himachal Pradesh
Source of Support: None, Conflict of Interest: None
OBJECTIVES: To describe the clinical profile of patient with bronchial asthma, to determine the presence of environmental risk factors among them and to determine the relationship between environmental risk factors to the severity of asthma.
METHODS: It was a descriptive observational study done at a tertiary care teaching hospital in sub-Himalyan belt of Northern India. Children aged 1-18 years,who presented to hospital with diagnosis of asthma were included in the study after obtaining informed consent.
RESULTS: Prevalence of asthma in children age 0-18 years was 1.6 % in this study.Mean age was 8.60±4.40 years with male preponderance. Majority of patients (68.3%) had onset of symptoms before 5 years of age. Fifty nine percent were malnourished and 53% had history of atopy. Majority of children were born vaginally (81.5%) with 91.5% of them were born at term with normal birthweight (90%) Asthma was more common in 2nd order birth (50.7%) and majority (60.7%) were bottle fed in first 6 months of life. Family history of atopy or asthma was present in 86% of the ptients. Eighty percent of patients had history of exacerbations episode after exposure to dust, 81.8% had seasonal variation of asthma with 52.3% exacerbations in winter. Seventy five percent had history of exacerbations during crop harvesting time.Seventy two percent had history of smoke producing fuel at home.Sixty percent had history of exposure to cigarette or other tobacco product smoke and 21.5% of pts had pets at home.Strong relationship was found between use of power and perfumes and exacerbations and exacerbation after exposure to cold air with uncontrolled asthma.
CONCLUSIONS: Male gender, malnourished and bottle fed children are prone for developing asthma. Presence of atopy, most commonly allergic rhinitis in early life predisposes children to asthma later in life. Exposure to cold air, dust during harvesting season and use of powder and perfumes are important risk factors for development of asthma.
Keywords: Bronchial asthma, environmental risk factors, sub-Himalyan belt
|How to cite this article:|
Rehalia N, Sharma J, Chaudhary S. Clinical profile and environmental risk factors of asthma in children at a tertiary care teaching hospital in the sub-Himalayan belt of Northern India. Indian J Allergy Asthma Immunol 2020;34:74-80
|How to cite this URL:|
Rehalia N, Sharma J, Chaudhary S. Clinical profile and environmental risk factors of asthma in children at a tertiary care teaching hospital in the sub-Himalayan belt of Northern India. Indian J Allergy Asthma Immunol [serial online] 2020 [cited 2020 Nov 24];34:74-80. Available from: https://www.ijaai.in/text.asp?2020/34/2/74/300922
| Introduction|| |
Asthma is a chronic inflammatory disorder of the airways characterized by obstruction of airflow, which may be completely or partially reversed with or without specific therapy. It is a common chronic disease of childhood and is the leading cause of childhood morbidity from chronic disease as measured by school absences, emergency department visits, and hospitalizations.
It is associated with airway hyper responsiveness (the airways narrow in an exaggerated fashion after being exposed to a trigger) and variable airflow obstruction. Over 300 million people worldwide are affected by asthma, with a high negative impact on quality of life, productivity, and health-care costs. Evidence shows that the prevalence of asthma is increasing, especially in children.
There has been a noticeable increase in the health-care burden due to asthma globally. The prevalence and mortality from asthma have shown an upward trend during an era when quality medications are easily available for asthma.
It has increased prevalence in the past 15 years in children. It affects 1%–18% of population in different countries. According to recent statistics, 14% of children over the world experience symptoms of asthma. In India, there are wide variations region wise in the prevalence of childhood asthma.
Asthma, like other chronic diseases, is a complex disease and heterogeneous in its origins and clinical expression. It results from the interaction of multiple genetic, epigenetic, and environmental factors.
Risk factors are genetic predisposition (family history of atopy or asthma), perinatal factors (low birth weight and prematurity), exposure to allergens, infections (respiratory infections, especially those caused by respiratory syncytial virus), environmental factors (air pollution and tobacco smoke), diet, and obesity.
Bronchial asthma has higher incidence in children living in Western countries, with “Hygiene hypothesis” proposed to be one of the important causes of bronchial asthma in children living in Western countries.
Asthma is defined by the history of respiratory symptoms such as wheeze, shortness of breath, chest tightness, and cough that vary over time and in intensity, together with variable expiratory airflow limitation.
Asthma falls into two broad categories: atopic (extrinsic) and nonatopic (intrinsic). The mechanisms behind atopic asthma are generally better understood than those of nonatopic asthma. While carriers of both of these types of asthma present with roughly the same symptoms, attacks are generally triggered by different environmental factors in each. Atopic triggers include known allergens such as pollen, mold, dander, and other allergic triggers. Triggers of attacks of nonatopic asthma include cold air, poor air quality, certain viruses, airborne insecticides, and other irritating substances.
Substantial increase in the incidence of asthma over the past few decades, geographic variation, and prevalence rates, supports the hypothesis that environmental factors may play an important role.
Because adequate data on this subject are not available in this sub-Himalayan belt of Himachal Pradesh (India), the present study was planned with the objective of understanding the clinical profile of childhood asthma and environmental risk factors for it.
The objectives were to describe the clinical profile of patients with bronchial asthma, to determine the presence of environmental risk factors among them, and to determine the relationship between environmental risk factors and the severity of asthma.
| Materials and Methods|| |
It was a descriptive observational study done at a tertiary care teaching hospital in the sub-Himalayan belt of Northern India.
Children aged 1–18 years, who presented to the hospital with a diagnosis of asthma were included in the study after obtaining informed consent from the parents and adolescents.
One hundred and thirty children of asthma were recruited for the purpose of study. The sample was calculated using EpiInfo 7 software (center for Disease Control and Prevention CDC, Atlanta, Georgia, United states), assuming prevalence rate of asthma 13.9%, confidence limit 5 % and confidence level of 90 %.
Diagnosis of asthma was made as per care definition and spirometry. In children <5 years, diagnosis was made as per stringent Asthma Preventive Index. Patients with shortness of breath of cardiac origin, with evidence of active concomitant pulmonary disease other than asthma and with evidence of concomitant chronic systemic disease, were excluded from the study.
Detailed history of the patients was obtained regarding demography (age, gender, socioeconomic status [SES] etc.), birth history, allergy history (allergy to dust, food, etc., allergic rhinitis/dermatitis), asthma symptoms, and environmental risk factors. Detailed clinical examination was done including anthropometry. Spirometry was done in all children above the age of 6 years.
| Results|| |
The present study was aimed to evaluate the clinical profile and environmental risk factors of asthma in children at a tertiary care teaching hospital in the sub-Himalayan belt of Northern India. A total of 130 children with asthma were included in the study. Out of these 130 patients, 67 patients needed admission and 16 required intensive care. The results of the study were as follows:
In the present study, we found that a total of 8050 patients of age 1–18 years presented in the pediatric department over a period of 1 year with respiratory illness. Out of these total patients, 130 patients had asthma. Thus, the prevalence of asthma in this sub-Himalayan belt, as per this hospital-based study, is 1.6% of children presenting with respiratory illness aged 1–18 years.
The clinical profile and environmental risk factors in this study group are as follows:
Patients' age ranged from 3 to 17 years, with a mean age of 8.60 ± 4.40 years. Nearly 50% (n = 65) of the patients were from age 3–7 years, 28.4% (n = 37) were from age group 8–12 years, and rest 21.5% (n = 28) were from 13 to 17 years [Table 1].
Age at onset of symptoms
In 47% of the patients (n = 62), age of the onset of symptoms was between 1 and 5 years. Nearly 20.7% of the patients had onset of symptoms in <1 year of age and rest 31.5% of the patients had onset after 5 years of age [Table 2].
|Table 2: Distribution of Patients on the basis of age of onset of Symptoms|
Click here to view
In the present study, 68.46% (n = 89) of the patients were male, while the remaining patients were female.
The present study observed that 77 (59.2%) children were malnourished, 49 (37.6%) patients had normal body mass index, and 4 (3%) children were overweight.
Associated history of atopy was present in 69 (53%) of the total patients. In all the patients with atopy, history of allergic rhinitis was present, while 41 patients with allergic rhinitis had associated allergic dermatitis and 20 patients had associated food allergy [Table 3].
One hundred and nineteen children were born at term and 11 were preterm. A total of 106 were born by normal vaginal delivery (NVD), 20 children were born via elective cesarean section, and 4 by emergency cesarean section. A total of 117 children had normal birth weight, while there were 13 children with low birth weight.
In our study, 66 (50.7%) children were second in birth order. Fifty (38.4%) children were born in first order, while 13 (10%) were third in birth order and one was fourth in birth order.
History of bottle feeding
Seventy-nine (60.7%) patients had a history of bottle feeding. Only 39.2% of the patients were exclusively breast fed in the first 6 months of life.
Socioeconomic status and overcrowding
As per Modified Kuppuswamy scale, 35.38% of the patients (n = 46) were from low SES, 40% (n = 52) were from middle class, while 24.61% of the patients (n = 32) were from upper class. Overcrowding in home was present in 26.9% of the patients.
In our study, 86 (66%) patients had a positive family history of asthma and 27 (20.7%) had a family history of atopy.
Environmental risk factors
One hundred and four patients (80%) had a history of exacerbation after exposure to dust. Sixty-eight (52.3%) patients had exacerbations mainly in the winter season. Ninety-seven (74.6%) patients had a history of increased symptoms in harvesting season. Smoke-producing fuel use and smoking in family were risk factors in 94 (72.3%) and 87 (66.9%) patients, respectively. Powder and perfume use and pets in home were the risk factors in 77 (59.2%) and 28 (21.5%) patients, respectively [Table 4]a.
The relationship between environmental risk factors and the severity of the disease
In our study, we found a strong relationship between the use of powder and perfumes and exacerbation after exposure to cold air with uncontrolled asthma with P < 0.05 [Table 4]b and [Table 4]c.
| Discussion|| |
The present study was aimed to evaluate the clinical profile and environmental risk factors of asthma in children at the department of pediatrics in a tertiary care teaching hospital in the sub-Himalayan belt of Northern India. This study was carried out on 130 patients. The results of the study are discussed as follows:
According to the current hospital-based study, the prevalence of asthma in this sub-Himalayan belt is 1.6% of children presenting with respiratory illness aged 1–18 years.
Age of patients
Patients with asthma who presented to the pediatric outpatient department of this tertiary care teaching hospital ranged from the age of 3 years to 17 years with a mean age of 8.60 ± 4.40 years.
Pal et al., in their study on the prevalence of asthma in children, reported that childhood asthma among children 6–7 years of age (6%) was higher than that of the older children of 13–14 years of age (4.5%).
Age of onset of symptoms
Though patients included were diagnosed at the age of 3 years or more, our study have found that 20.7% of the patients had onset of symptoms in <1 year of age, 47.69% had onset between 1 and 5 years, and the rest 31.5% had onset after 5 years of age. Radhakrishnan et al. found a higher risk of being diagnosed as asthmatic in the first 3 years of life among children born after 1996 compared to those born between 1993 and 1995.
In this study, there was a male preponderance with a male-to-female ratio of 2.1:1. Sex variations in asthma have been reported in many studies. Pal et al. reported male predominance in children with asthma in their study. They found that boys had a significantly higher prevalence of asthma as compared to girls (12.8% and 10.7%, respectively). Behl et al. have shown that boys had higher prevalence (3.1%) than girls (1.4%). Vyankatesh et al. found that females were having more prevalence as that of males, with the ratio being 1:1.5 (male:female). Vyankatesh et al. found that female were having more prevalence as that of males, with the ratio being 1:1:5(male: female) The mechanisms behind this age–sex interaction have not yet been established, but differences in hygiene practices between younger males and females have been proposed as a factor. It has also been suggested that lung size and growth, physician diagnostic practices, and hormonal changes during puberty may explain the differences in asthma risk between young males and females.
In this study, 59.2% of the patients were malnourished and only 4 out of 130 (3%) patients were overweight. Stojanovic et al. reported that lower percentage of muscle mass is associated with more exacerbations and obstruction in asthma. With more systemic inflammation, malnutrition has greater role, as in asthma with airflow obstruction.
Granell et al. have shown that increasing rates of obesity and overweight in the Western world have been roughly paralleled by increases in asthma and other atopic diseases. Shore have concluded that asthma is more frequently observed in obese individuals. An increase in intra-abdominal pressure on the diaphragm and fat mass on chest wall leads to mass loading of the thorax, resulting in a reduction of respiratory compliance and changes in airway resistance. Figueroa-Muñoz et al. further described that systemic and airway inflammation of obesity and asthma are interlinked by systemic spillover of “adipokines.”
In this study, associated history of atopy was present in 53% (69) of the total patients. In all the patients with atopy, a history of allergic rhinitis was present, while 41 patients with allergic rhinitis had associated allergic dermatitis and 20 patients had associated food allergy.
Pearce et al. in their study described that, asthma has a strong atopic component and is considered to be strongly related to other atopic diseases. It has been suggested that approximately half of the asthma cases are related to atopy. Ober and Yao, concluded that atopic dermatitis and food allergy typically develop in infancy followed by asthma and/or allergic rhinitis in childhood. The vast majority (~80%) of patients with asthma have allergic rhinitis, whereas 19%–38% of patients with allergic rhinitis have coexisting asthma.
Ninety-one percent of the children included in the study, were born at term gestation and 90% had normal birth weight. Eighty-one percent were born by NVD, 15.3% by elective cesarean section, and only 3% were born by emergency lower segment cesarean section. Research done by Sonnenschein-van der Voort et al. has suggested that the adverse effect on lung development associated with young gestational age and low birth weight may predispose preterm and/or underweight infants to an increased risk of asthma and wheezing symptoms in later life. Nafstad et al. concluded that development of atopy was 2–3 times more likely among infants delivered by emergency cesarean section, although no such association occurred with elective cesarean section. However, no such association was seen in the present study, which may be due to more normal vaginal deliveries and term deliveries overall as compared to cesarean sections and preterm births in this sub-Himalayan belt.
Relation with birth order
In this study, asthma was found more common in second-order sibling. Out of the total patients included in this study, 50.7% were second in birth order followed by first-order births (38%).
The hygiene hypothesis posits that exposure of an infant to a substantial number of infections and many types of bacteria stimulates the developing immune system toward nonasthmatic phenotypes. This may be exemplified in the real world by large family size, whereby later-born children in large families would be expected to be at lower risk of asthma than first-born children, because of exposure to their older siblings' infections. However, in our study, asthma was more in younger siblings than elder.
Sixty-one patients included in the study had a history of bottle feeding and only 39.2% were exclusively breast fed in the first 6 months of life.
The influence of breastfeeding on the risk of childhood atopy and asthma remains controversial. Breast milk contains compounds that confer benefits to a child's passive immune system (e.g., through secretory immunoglobin-G) while also enhancing active immune response in infants. However, variation in the constituents of breast milk between mothers means that these effects may vary significantly between individuals.
Bergmann et al. and Dell et al. have also shown protection,, whereas others have reported higher rates of allergy and asthma among breastfed children.,
In this study, it was found that 35.38% of the patients were from low SES. Twenty-seven percent of the patients had a history of overcrowding in their living places. Sharma et al. in their study found that 44% of the patients were from poor SES. Some studies have suggested that increasing family SES indicated by higher parental education, parental occupational prestige, and family income are either related to an increased risk of childhood asthma. Other studies have shown a reversal effect, with lower SES levels generally increasing the risk of asthma and wheeze rather than decreasing it.,
Twenty-seven percent of the patients had a history of overcrowding in their living places. Family size and the number and order of siblings may affect the risk of development of asthma. This can be explained on the basis of hygiene hypothesis.
In this study, 86% of the patients had a family history of asthma or atopy. Out of these, 66% of the patients had a family history of asthma and 21.5% of the patients had a family history of atopy. Having a family history of asthma or atopy has been consistently shown to be a predictor of asthma and wheeze in childhood. Alford et al. and Arshad et al. have specifically investigated these effects and found a positive association.,
Environmental risk factors
Eighty percent of the patients in this study had a history of exacerbation episode after exposure to dust. This can be related to increase in air pollution. As children spend more time outdoors and do not have a fully developed immune system, they are more susceptible to poor quality of air. Many studies have reported higher prevalence of childhood asthma and wheezing symptoms in urban rather than rural areas due to increase in dust and air pollution.
It was found that 81.8% of the patients had seasonal variation of asthma. Out of these patients, 52.3% had exacerbations in winters and 28.4% had a history of exacerbation in rainy season. Sharma et al. in their study identified seasonal variation as a risk factor for exacerbation in 86% of children.
In this study, 74.6% of the patients had a history of exacerbations during crop harvesting time. It can be related to the poor quality of air. Many studies assessing long- and short-term exposure to different pollutants and respiratory outcomes have been conducted to date. Shau – Ju et al and Gowers et al. described the biological mechanisms by which air pollution may contribute to the risk of asthma attacks, asthma induction, wheeze and include oxidative stress, airway damage, increasing inflammation and sensitization to allergens.,
Use of smoke-producing fuel
In this study, 72.3% of the patients had a history of using smoke-producing fuel at home. A study done by Sharma et al. found that asthma was more in children living in homes with usage of smoke-producing fuel (70%).
Smoker in family
History of cigarette smoking or other tobacco product smoking was present in 66.9% of the patients in this study.
Awasthi et al. found that father smoking >5 bidis indoor was associated with persistent asthma. Burke et al. suggested that exposure to passive smoke (also known as environmental tobacco smoke or second-hand smoke), either prenatally or postnatally, has been widely studied as a risk factor for childhood asthma, partly due to it being an avoidable and generally removable risk. Passive exposure to the smoke emitted by cigarettes and other tobacco products has been shown to have a negative effect on nearly every organ of the human body. For this reason, passive smoke exposure is widely accepted as a risk factor for childhood asthma.
Use of powder and perfumes
Fifty-two percent of the patients in this study, had a history of use of powder and perfumes. Fragranced products emit a range of volatile and semi-volatile compounds which are harmful for both asthmatics and nonasthmatics, with more effect on asthmatics. They can lead to headache, respiratory problems, and exacerbation of asthma.
Pets in home
In this study, it was found that 21.5% of the patients had pets in home. Spengler et al. described household exposure to household allergens such as dust mite, cockroaches, pet dander, and other vermin has been shown to be risk factor for the induction of asthma and wheeze in children.
| Conclusion|| |
The present study on childhood asthma concluded that male gender and malnourished and bottle-fed children are more prone for developing asthma. Presence of atopy, most commonly allergic rhinitis in the early period of life, can predict the development of asthma later on, and majority of the patients have onset of symptoms within the first 5 years of life, thus these children should be followed up for early diagnosis. Exposure to cold air and dust during harvesting season are important risk factors for exacerbation in this sub-Himalayan belt. Use of powder and perfumes and exacerbation after exposure to cold air were found to be strongly related with uncontrolled asthma. Thus, it is to be recommended that use of powder and perfumes by patients with asthma and their family members should be avoided and efforts should be made by parents to decrease the exposure of child to cold air.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Masoli M, Fabian D, Holt S, Beasley R. The global burden of asthma, executive summary of the GINA Dissemination Committee report. Allergy 2004;59:469-78.
Lieu TA, Lozano P, Finkelstein JA, Chi FW, Jensvold NG, Capra AM, et al
. Racial/ethnic variation in asthma status and management practices among children in managed medicaid. Pediatrics 2002;109:857-65.
Jindal SK, Gupta D, Aggarwal AN, Agarwal R. World Health Organization, Government of India. Guidelines for the management of asthma at the primary and secondary levels of health care in India. Indian J Chest Dis Allied Sci 2005;47:309-43.
Masoli M, Fabian D, Holt S, Beasley R; Global Initiative for Asthma (GINA) Program. The global burden of asthma: Executive summary of the GINA Dissemination Committee report. Allergy 2004;59:469-78.
Blumenthal MN. Genetic, epigenetic, and environmental factors in asthma and allergy. Ann Allergy Asthma Immunol 2012;108:69-73.
Bracken MB, Belanger K, Cookson WO, Triche E, Christiani DC, Leaderer BP. Genetic and perinatal risk factors for asthma onset and severity: A review and theoretical analysis. Epidemiol Rev 2002;24:176-89.
Subbarao P, Mandhane PJ, Sears MR. Asthma: Epidemiology, etiology and risk factors. CMAJ 2009;181:E181-90.
Behl RK, Kashyap S, Sarkar M. Prevalence of bronchial asthma in school children of 6-13 years of age in Shimla city. Indian J Chest Dis Allied Sci 2010;52:145-8.
Global Strategy for Asthma Management and Prevention. Global Initiative for Asthma. Global Strategy for Asthma Management and Prevention; 2017. p. 14-7.
Castro-Rodríguez JA, Holberg CJ, Wright AL, Martinez FD. A clinical index to define risk of asthma in young children with recurrent wheezing. Am J Respir Crit Care Med 2000;162:1403-6.
Pal R, Dahal S, Pal S. Prevalence of bronchial asthma in Indian children. Indian J Community Med 2009;34:310-6.
] [Full text]
Radhakrishnan DK, Dell SD, Guttmann A, Shariff SZ, Liu K, To T. Trends in the age of diagnosis of childhood asthma. J Allergy Clin Immunol 2014;134:1051-62.
Pal R, Barua A. Prevalence of childhood bronchial asthma in India. Ann Trop Med Public Health 2008;1:73-5. [Full text]
Vyankatesh AA, Bharat PS, Kush A. Prevalence of Asthma in school going children of Semi Urban Area in the state of Madhya Pradesh, IND J Med. Public Health 2017;7:37-40.
Stojanovic Z, Martinez C, Rivera, Centeno C, Molins E, Sanchez E, et al
. Nutritional aspects and asthma. Influence of malnutrition factors on severity of asthma. Eur Respir J 2012;40:501.
Granell R, Henderson AJ, Evans DM, Smith GD, Ness AR, Lewis S, et al
. Effects of BMI, fat mass, and lean mass on asthma in childhood: A Mendelian randomization study. PLoS Med 2014;11:e1001669.
Shore SA. Obesity and asthma: Implications for treatment. Curr Opin Pulm Med 2007;13:56-62.
Figueroa-Muñoz JI, Chinn S, Rona RJ. Association between obesity and asthma in 4-11 year old children in the UK. Thorax 2001;56:133-7.
Pearce N, Pekkanen J, Beasley R. How much asthma is really attributable to atopy? Thorax 1999;54:268-72.
Ober C, Yao TC. The genetics of asthma and allergic disease: A 21st
century perspective. Immunol Rev 2011;242:10-30.
Sonnenschein – Vander Voort AM, Arends LR, DE Jongste JC, et al.
Preterm birth, infant weight gain and childhood Asthma risk: a meta – Analysis of 147,00 European children, J Allergy Clin Immunol 2014;133:1317-29.
Nafstad P, Magnus P, Jaakkola JJ. Risk of Childhood Asthma and Allergic rhintis in relation to pregnancy complication. J Allergy Chinical Immunol 2000:106:867- 73.
Schaub B, Lauener R, von Mutius E. The many faces of the hygiene hypothesis. J Allergy Clin Immunol 2006;117:969-77.
Bergmann RL, Diepgen TL, Kuss O. Breastfeeding duration is a risk factor for atopic eczema. Clin Exp Allergy 2002;32:205-9.
Dell S, To T. Breastfeeding and asthma in young children: Findings from a population-based study. Arch Pediatr Adolesc Med 2001;155:1261-5.
Sears MR, Greene JM, Willan AR. Long-term relation between breastfeeding and development of atopy and asthma in children and young adults: A longitudinal study. Lancet 2002;360:901-7.
Sharma S, Sood M, Sood A. Environmental risk factors in relation to childhood asthma in rural area. Curr Pediatr Res 2011;15:29.
Spengler JD, Jaakkola J, Parise H, Katsnelson BA, Privalova LI, Kosheleva AA. Housing characteristics and children's respiratory health in the Russian Federation. Am J Public Health 2004;94:657-62.
Shau-Ku H, Zhang Q, Qiu Z, Fan CK. Mechanistic impact of outdoor air pollution on asthma and allergic diseases. J Thorac Dis 2015;7:23-33.
Alford SH, Zoratti E, Peterson EL, Maliarik M, Ownby DR, Johnson CC. Asthma diagnosis and treatment: Parental history of atopic disease: Disease pattern and risk of pediatric atopy in offspring. J Allergy Clin Immunol 2004;114:1046-50.
Arshad SH, Karmaus W, Raza A, Kurukulaaratchy RJ, Matten SM, et al
. Rhintis, Sinusitis and upper airway disease: The Effect of parental allergy on childhood allergic disease depends on sex of the child. J Allergy clin Immunol 2012;130:427-34.
Gowers AM, Cullinan P, Ayres JG, Anderson HR, Strachan DP, Holgate ST, et al
. Does outdoor air pollution induce new cases of asthma? Biological plausibility and evidence; A review. Respirology 2012;17:887-98.
Awasthi S, Gupta S, Maurya N, Tripathi P, Dixit P, Sharma N. Environmental risk factors for persistent asthma in Lucknow. Indian Pediatr 2012;70:1311-31.
Burke H, Leonardi-Bee J, Hashim A, Pine-Abata H, Chen Y, Cook DG. Prenatal and passive smoke exposure and incidence of asthma and wheeze systematic review and metaanalysis. Pediatrics 2012;129:735-44.
[Table 1], [Table 2], [Table 3], [Table 4]