Why are rates of asthma in developed countries higher now than in the past?

42 - The Epidemiology of Asthma

2019, Kendig's Disorders of the Respiratory Tract in Children

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Epidemiology is the study of populations to discover modifiable factors that contribute to disease occurrence and natural history with a view to reducing disease burden through prevention. Asthma is a complex, polygenic disease with heterogeneous manifestations making it difficult to define precisely in population studies. Despite this, global efforts to harmonize outcome definitions have led to detailed understanding of the temporal and spatial variations of asthma prevalence in children. Asthma prevalence notably increased in high-income countries during the final three decades of the 20th century, but the cause for this has never been fully established.

Early life has been implicated as a critical period for the development of asthma. Many environmental influences have been considered as potential risk factors for asthma, but few have been associated with more than modest increases in risk. One barrier to identifying causal risk factors is the clustering of environmental factors with consequent confounding of relationships between environment and disease. Thus even strong and reproducible associations can seldom be regarded as causal without experimental evidence, which is generally lacking.

Despite these difficulties, new approaches to asthma classification, meticulous observations in birth cohorts, technological advances that enable assignment or genetic risk and identification of biomarkers for disease pathways, and analytical advances have contributed to real advances in understanding asthma pathogenesis. The interaction of allergic sensitization with respiratory viral infections offers a promising target for the development of preventative interventions.

Evidence in immunotherapy for paediatric respiratory allergy: Advances and recommendations

2016, Allergologia et Immunopathologia

Citation Excerpt :

Allergic respiratory diseases are a major health problem in the paediatric population due to their high level of prevalence and chronicity, as well as to their relevance in both the cost of healthcare and the quality of life of the patients and their families. According to large population-based studies, the prevalence of asthma and allergic rhinitis (AR) in children has increased in recent decades, presenting wheezing in the past year in up to 12% of children aged 6–7 years and to 14% at 13–14 years; AR has a prevalence of 15%.1–3 The total costs of asthma are greater in children than in adults due to the greater severity of the disease in this population,4 decreasing their quality of life in terms of health.5

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Allergic respiratory diseases are major health problems in paediatric population due their high level of prevalence and chronicity, and to their relevance in the costs and quality of life. One of the most important risk factors for the development of airway diseases in children and adolescents is atopy. The mainstays for the treatment of these diseases are avoiding allergens, controlling symptoms, and preventing them through sustained desensitization by allergen immunotherapy (AIT). AIT is a treatment option that consists in the administration of increasing amounts of allergens to modify the biological response to them, inducing long-term tolerance even after treatment has ended. This treatment approach has shown to decrease symptoms and improve quality of life, becoming cost effective for a large number of patients. In addition, it is considered the only treatment that can influence the natural course of the disease by targeting the cause of the allergic inflammatory response. The aim of this publication is to reflect the advances of AIT in the diagnosis and treatment of allergic respiratory diseases in children and adolescents reviewing articles published since 2000, establishing evidence categories to support the strength of the recommendations based on evidence. The first part of the article covers the prerequisite issues to understand how AIT is effective, such as the correct etiologic and clinical diagnosis of allergic respiratory diseases. Following this, the article outlines the advancements in understanding the mechanisms by which AIT achieve immune tolerance to allergens. Administration routes, treatment regimens, dose and duration, efficacy, safety, and factors associated with adherence are also reviewed. Finally, the article reviews future advances in the research of AIT.

Thermal and environmental conditions in Shanghai households: Risk factors for childhood health

2016, Building and Environment

Citation Excerpt :

Many epidemiological studies have demonstrated an increase in allergic diseases in the past 40 years worldwide [1–3].

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An overall investigation of children’s health status, residential thermal environment, and pollutants was conducted in the homes primary school children during winter and summer in Shanghai, China. The houses were divided into Group A (unhealthy child living) and Group B (healthy child living). During a two-week monitoring period in winter, indoor temperatures in Group A were significantly lower than in Group B (1–2 °C; p < 0.001). Relative humidity (RH) of Group A were 5–8% higher than Group B (p < 0.001), and the ratio of RH > 70% of Group A was around 0.6 in winter. Bad thermal environment in Group A was a risk factor for children’s health. Average winter CO2 concentrations were 758 ppm in Group A and 701 ppm in Group B, and the houses had poor ventilation during nighttime. Indoor concentrations of formaldehyde (HCHO), acetaldehyde and TVOC generally satisfied the Chinese national standards. However, indoor PM2.5 and PM10 concentrations in Group A were higher than those of Group B, and PM concentrations in all investigated houses exceeded the Chinese national standards in winter. Dibutyl phthalate (DBP) and Di (2-ethylhexyl) phthalate (DEHP) in house dust of four living rooms showed very high concentrations (3–4 times the EU recommended limit of 1000 μg/g). Aspergillus and Cladosporium in room air and house dust were linked to high RH, and could be suspected association with poor children’s health. This study provides comprehensive information on indoor thermal and environmental conditions in houses in Shanghai, and their exposures of primary schoolchildren to these health risks.

Role of Vaccines

2016, Allergy, Immunity and Tolerance in Early Childhood: The First Steps of the Atopic March

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Active immunizations against diseases that cause substantial morbidity or potential mortality represent one of the greatest advances in medicine over the past century. Allergic patients should receive the same publicly recommended vaccines unless there is an allergy-specific risk that outweighs the risk of the infectious disease to be prevented.

Prevalence of childhood asthma in Ulaanbaatar, Mongolia in 2009

2016, Allergology International

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Bronchial asthma is a common but important chronic disease in children in all over the world. To take measures against prevalence of childhood asthma, many researchers have surveyed the actual statuses of childhood asthma in developed countries, but in most Asia–Pacific developing countries including Mongolia such surveys have never been sufficiently conducted until now. We have thought that this survey, though performed in 2009, will give important and meaningful information even now in taking measures to prevent prevailing bronchial asthma in children in Mongolia or the countries under similar statuses.

The asthma prevalence and patient background information in Mongolian children aged 6–7 living in Ulaanbaatar were examined using a written questionnaire modified for their parents from that prepared by the International Study of Asthma and Allergies in Childhood (ISAAC).

The estimated prevalence of asthma in Mongolian children was 20.9%. The following 3 risk factors were found to be related to asthma: (1) having allergic rhinitis symptoms, (2) mothers' smoking, and (3) history of severe respiratory infection before 1-year-old.

The asthma prevalence in Mongolian children was higher than that in the world and Asia–Pacific countries reported by ISAAC. The higher prevalence was probably attributable to households' (especially mothers) smoking in draft-free houses designed for the cold area and severe air-pollution due to rapid industrialization and urbanization in Mongolia. Smoking prohibition in the mother (including family members) and a reduction of exposure to air pollutants are urgently needed to prevent developing childhood asthma.

Primary pollutants in schoolchildren's homes in Wuhan, China

2015, Building and Environment

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In 2013, field campaigns were performed in the naturally ventilated homes of ten schoolchildren living in Wuhan's urban area, with purpose to ascertain the primary indoor pollutants that have been associated with respiratory and allergic health in children. According to the 2-week monitoring, mean temperature and relative humidity were 19.5 °C and 60% in autumn and 12.7 °C and 55% in winter, respectively; mean level of carbon dioxide (CO2) was 525 ppm in autumn and 748 ppm in winter. Particulate matter (PM) led to the most severe indoor air pollution with 94% of gravimetric concentrations of PM2.5 far beyond 75 μg/m3. Indoor/outdoor (I/O) ratio of PM2.5 level varied between 0.72 and 1.04; furthermore, statistical analysis proved that indoor PM level was significantly associated with outdoor level (R2 ≥ 0.93, p < 0.001, n = 16). Formaldehyde and acetaldehyde in air samples were always at the levels far below the recommended limits, 100 μg/m3 and 48 μg/m3, respectively; but total volatile organic compounds (TVOCs) were higher than the national standard of 600 μg/m3 in some homes. Furthermore, high levels of di(2-ethylexyl) phthalate (DEHP) and dibutyl phthalate (DBP) were frequently detected in house dust. The results showed that airborne Aspergillus and Penicillium caused some concerns of fungal pollution in autumn. In conclusion, in the homes of the schoolchildren in Wuhan's urban area, airborne PM, and DEHP and DBP in house dust are primary pollutants; sometimes TVOCs also lead to indoor air pollution; in addition, airborne fungal components indicate to be a contributing factor to indoor pollution of concern in warm environment.

Research article

Cooking fuels and prevalence of asthma: a global analysis of phase three of the International Study of Asthma and Allergies in Childhood (ISAAC)

The Lancet Respiratory Medicine, Volume 1, Issue 5, 2013, pp. 386-394

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Indoor air pollution from a range of household cooking fuels has been implicated in the development and exacerbation of respiratory diseases. In both rich and poor countries, the effects of cooking fuels on asthma and allergies in childhood are unclear. We investigated the association between asthma and the use of a range of cooking fuels around the world.

For phase three of the International Study of Asthma and Allergies in Childhood (ISAAC), written questionnaires were self-completed at school by secondary school students aged 13–14 years, 244 734 (78%) of whom were then shown a video questionnaire on wheezing symptoms. Parents of children aged 6–7 years completed the written questionnaire at home. We investigated the association between types of cooking fuels and symptoms of asthma using logistic regression. Adjustments were made for sex, region of the world, language, gross national income, maternal education, parental smoking, and six other subject-specific covariates. The ISAAC study is now closed, but researchers can continue to use the instruments for further research.

Data were collected between 1999 and 2004. 512 707 primary and secondary school children from 108 centres in 47 countries were included in the analysis. The use of an open fire for cooking was associated with an increased risk of symptoms of asthma and reported asthma in both children aged 6–7 years (odds ratio [OR] for wheeze in the past year, 1·78, 95% CI 1·51–2·10) and those aged 13–14 years (OR 1·20, 95% CI 1·06–1·37). In the final multivariate analyses, ORs for wheeze in the past year and the use of solely an open fire for cooking were 2·17 (95% CI 1·64–2·87) for children aged 6–7 years and 1·35 (1·11–1·64) for children aged 13–14 years. Odds ratios for wheeze in the past year and the use of open fire in combination with other fuels for cooking were 1·51 (1·25–1·81 for children aged 6–7 years and 1·35 (1·15–1·58) for those aged 13–14 years. In both age groups, we detected no evidence of an association between the use of gas as a cooking fuel and either asthma symptoms or asthma diagnosis.

The use of open fires for cooking is associated with an increased risk of symptoms of asthma and of asthma diagnosis in children. Because a large percentage of the world population uses open fires for cooking, this method of cooking might be an important modifiable risk factor if the association is proven to be causal.

BUPA Foundation, the Auckland Medical Research Foundation, the Health Research Council of New Zealand, the Asthma and Respiratory Foundation of New Zealand, the Child Health Research Foundation, the Hawke's Bay Medical Research Foundation, the Waikato Medical Research Foundation, Glaxo Wellcome New Zealand, the NZ Lottery Board, Astra Zeneca New Zealand, Hong Kong Research Grant Council, Glaxo Wellcome International Medical Affairs.

Research article

Asthma Phenotypes: Nonallergic (Intrinsic) Asthma

The Journal of Allergy and Clinical Immunology: In Practice, Volume 2, Issue 6, 2014, pp. 650-652

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The definition of nonallergic asthma includes that subset of subjects with asthma and with whom allergic sensitization cannot be demonstrated. These individuals should have negative skin prick test or in vitro specific-IgE test to a panel of seasonal and perennial allergens. Nonallergic asthma occurs in 10% to 33% of individuals with asthma and has a later onset than allergic asthma, with a female predominance. Nonallergic asthma appears to be more severe than allergic asthma in many cases and may be less responsive to standard therapy. Although many of the immunopathologic features of nonallergic asthma are similar to those observed with allergic asthma, some differences have been described, including a higher expression of RANTES in mucosa and bronchoalveolar lavage fluid, as well as a higher GM-CSF receptor alpha expression. Unbiased statistical methods, such as cluster analysis and latent class analysis, indicate that the lack of atopy is not the most important defining factor in assigning an individual to many specific phenotypes but rather is more important in some phenotypes than others, and appears to modulate the clinical expression of the disease. Despite an appreciation of this clinical entity for many years, many of its clinical implications remain unclear.

Research article

Increased Risk of Exacerbation and Hospitalization in Subjects With an Overlap Phenotype: COPD-Asthma

Chest, Volume 145, Issue 2, 2014, pp. 297-304

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Several COPD phenotypes have been described; the COPD-asthma overlap is one of the most recognized. The aim of this study was to evaluate the prevalence of three subgroups (asthma, COPD, and COPD-asthma overlap) in the Latin American Project for the Investigation of Obstructive Lung Disease (PLATINO) study population, to describe their main characteristics, and to determine the association of the COPD-asthma overlap group with exacerbations, hospitalizations, limitations due to physical health, and perception of general health status (GHS).

The PLATINO study is a multicenter population-based survey carried out in five Latin American cities. Outcomes were self-reported exacerbations (defined by deterioration of breathing symptoms that affected usual daily activities or caused missed work), hospitalizations due to exacerbations, physical health limitations, and patients' perception of their GHS obtained by questionnaire. Subjects were classified in three specific groups: COPD—a postbronchodilator (post-BD) FEV1/FVC ratio of < 0.70; asthma—presence of wheezing in the last year and a minimum post-BD increase in FEV1 or FVC of 12% and 200 mL; and overlap COPD-asthma—the combination of the two.

Out of 5,044 subjects, 767 were classified as having COPD (12%), asthma (1.7%), and COPD-asthma overlap (1.8%). Subjects with COPD-asthma overlap had more respiratory symptoms, had worse lung function, used more respiratory medication, had more hospitalization and exacerbations, and had worse GHS. After adjusting for confounders, the COPD-asthma overlap was associated with higher risks for exacerbations (prevalence ratio [PR], 2.11; 95% CI, 1.08-4.12), hospitalizations (PR, 4.11; 95% CI, 1.45-11.67), and worse GHS (PR, 1.47; 95% CI, 1.18-1.85) compared with those with COPD.

The coexisting COPD-asthma phenotype is possibly associated with increased disease severity.

Research article

Changes in the prevalence of asthma and related risk factors in adolescents: Three surveys between 1994 and 2015

Allergologia et Immunopathologia, Volume 47, Issue 4, 2019, pp. 313-321

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This study assesses the temporal trend of current asthma symptoms prevalence and associated factors in Chilean adolescents from South-Santiago, considering surveys performed in 1994, 2002 and 2015.

The prevalence of current asthma symptoms showed a trend to increase from 11.1% in 1994 to 13.4% in 2015 (p < 0.001); physician-diagnosed asthma increased from 11.5% to 13.8%, (p < 0.001) whereas severe asthma and asthma with exercise decreased (p < 0.001). Female adolescents had a higher prevalence of current asthma in the three surveys (p < 0.001), and was a risk factor for asthma in the three surveys. In 2002, frequent consumption of meat and potatoes were associated with current asthma while frequent vigorous exercise was protective. Frequent exercise and parental tobacco smoking were risk for asthma in 2015 (p < 0.001). Current active tobacco smoking showed a trend to increase reaching a prevalence of 28.9% in 2015 (p < 0.001). There was a consistently low proportion of adolescents with current wheezing and asthma diagnosis (32.1% in 2015) and 37.6% of them had no asthma treatment.

The prevalence of current asthma in adolescents from the studied area would be still increasing. As in other studies, female adolescents had a higher prevalence of current asthma. Current active tobacco smoking has strikingly increased in the studied children while indoor passive tobacco exposure remains inadmissibly high. Our findings suggest that asthma in children is underdiagnosed and undertreated. More attention should be given to female gender, tobacco exposure, air pollution and local diagnostic preferences when studying and interpreting trends of asthma prevalence in adolescents from developing localities.

Research article

Measurement of vaccine confidence using media surveillance system

The Lancet Infectious Diseases, Volume 14, Issue 3, 2014, pp. 187-188

Research article

An international comparison of risk factors between two regions with distinct differences in asthma prevalence

Allergologia et Immunopathologia, Volume 46, Issue 4, 2018, pp. 341-353

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Investigation of the geographic variation in asthma prevalence can improve our understanding of asthma etiology and management. The purpose of our investigation was to compare the prevalence of asthma and wheeze among adolescents living in two distinct international regions and to investigate reasons for observed differences.

A cross-sectional survey of 13–14 year olds was completed in Saskatoon, Canada (n = 1200) and Skopje, Republic of Macedonia (n = 3026), as part of the International Study of Asthma and Allergies in Childhood (ISAAC) Phase 3 study. Surveys were self-completed by students following the ISAAC protocol. Multiple logistic regression models were used to investigate associations with reports of asthma and current wheeze. A mediation analysis was then completed.

Asthma prevalence was much higher in Saskatoon than Skopje (21.3% vs. 1.7%) as was the prevalence of current wheeze (28.2% vs. 8.8%). Higher paracetamol (acetaminophen) use was a consistent risk factor for asthma and wheeze in both locations and showed dose-response relationships. In both countries, paracetamol use and physical activity mediated some of the association for both asthma and wheeze. In Saskatoon, among those with current wheeze, 42.6% reported ever having a diagnosis of asthma compared to 10.2% among Skopje adolescents.

The results suggest that the variation in risk factors between the two locations may explain some of the differences in the prevalence of asthma and wheeze between these two study sites. However, diagnostic labeling patterns should not be ruled out as another potential explanatory factor.

Is asthma more common now than in the past?

Why are asthma rates rising?

What are the factors influencing the development and expression of asthma?

Is the rate of asthma increasing?