In all communities, poverty is strongly related to ill health 1. This has not generally been the pattern for asthma, where the lifetime prevalence of symptoms is usually higher in more affluent societies 2, 3, and a rising prevalence of asthma is a price paid for increasing national prosperity. This trend is probably inevitable since to date, no public health strategy for large-scale primary prevention of asthma has yet proved feasible or effective.
The favoured reason for this apparent protective effect of low socioeconomic status (SES) and/or of a rural lifestyle for atopy and asthma is the hygiene hypothesis, which, in its simplest form, suggests that early life exposure to microbial products modulates the immune response away from mechanisms related to the development of atopy 4, 5. In recent years, data from many studies have challenged this view 6. There have been consistent demonstrations of a positive association between lower SES and risk of wheezing in children and adolescents, both in high- and low/middle-income countries (LMICs), indicating a more complex interaction between factors, some protective and others causative. While dichotomising society into either “hygienic” and “unhygienic” is appealing, it is an obvious oversimplification of the environment in which we all live. More importantly, for healthcare planners, all communities are at risk of rapid change in the prevalence of asthma as living conditions change, and the largest increases are being observed in some LMICs with large populations 3. This represents a burden for which they are often ill-equipped. However, on more detailed review, the association between poverty and asthma prevalence is not fully understood and deserves further investigation.
POVERTY AND RISK OF ASTHMA
First of all a distinction must be made between risk of asthma ever (lifetime risk) and current symptoms 2. Gross national product per capita is generally associated with both an increasing prevalence of wheezing ever and wheezing in the last 12 months 7. However, the prevalence of current symptoms is modifiable by current exposures (to allergens and environmental pollution, as well as other factors) and by effective treatment. Thus, even where prevalence is low, the burden of disease may be high, and poverty emerges as an important risk factor for current symptoms of asthma. This might account for the high prevalence of asthma symptoms reported from several urban centres of Latin America where asthma is positively associated with low SES 8–11, and some underprivileged areas in high-income countries 12–17. da Cunha et al. 18 performed an ecological study of the relationship between the prevalence of wheezing and common health and socioeconomic indicators measured at the population level in 20 cities in Brazil. Only surveys using methods from the International Study of Asthma and Allergies in Childhood (ISAAC) were included. SES indicators that bore a direct association with asthma symptoms in both children (6–7 yrs of age) and adolescents (13–14 yrs of age) were poor sanitation, infant mortality and availability of hospital beds per 10,000 subjects. In children living in US inner cities, the burden of asthma is high and appears to be independent of ethnicity and income 15. In addition, the relationship between poverty and asthma may change over time. For example, a study from Sweden has shown a reversal of the association between SES and asthma prevalence; military conscripts of low SES had the lowest prevalence of asthma three decades ago but now have the highest prevalence, with prevalence increasing in successive generations 16. A study performed in Germany demonstrated that the prevalence of asthma was higher among parents of high SES, but no association of SES and asthma was observed in their children 17.
In the current issue of the European Respiratory Journal, Sembajwe et al. 19 report the relationship between gross national income in purchasing power parity (GNI PPP), the prevalence of symptoms and doctor diagnosis of asthma. The data was obtained from the World Health Survey performed in 64 countries from 2002 20. A bimodal distribution of asthma symptoms was observed, higher in high- and low-income countries, and lower in middle-income countries. How do these observations fit with previous reports? The first consideration is the U-shaped curve of prevalence of current wheezing; second is the discrepancy between current wheezing and a history of doctor-diagnosed asthma. Sembajwe et al. 19 correctly attribute the former to the higher prevalence of asthma in the high-income countries, and the second peak to a mix of factors: uncontrolled asthma, confounding respiratory conditions in communities with high levels of pollution, and respiratory infections that might give rise to wheezing 7. Furthermore, Sembajwe et al. 19 point to a wide range of prevalence of symptoms, even in high-income countries, probably reflecting the variation in SES and living conditions in each country. The variable correlations between wheezing symptoms and history of doctor-diagnosed asthma are also to be expected. In all asthma surveys, symptoms of asthma exceed previous asthma diagnosis, the ratio being positively correlated with the availability of health services and inversely related to societal and cultural factors such as social acceptability of a diagnosis of asthma 21. Another consideration is differences in the significance of symptoms of asthma in different communities, within and across country boundaries. For example, a comparison of associations between symptoms of asthma and features of allergic sensitisation in Russia versus Finnish Karelia has revealed differences that are attributed to the varying living conditions of children in these neighboring regions 22; however, they might be a consequence of a different perceptions of the disease. Wheezing may have different meanings in different countries, making international comparisons more difficult to interpret.
Interpretation of the relationship between asthma and GNI PPP in the study by Sembajwe et al. 19 is also limited by the paucity of information on other variables that may have an influence. First is inhomogeneity of populations within countries, and a secondly is the impact of urbanisation. As an example, Brazil, which has the highest reported prevalence of wheezing, is categorised as a middle-income country. This assessment is skewed by a small proportion of its very large population that has a high or very high income. A majority of the population are in the low-income category. This inequality is captured in figure 1⇓, which clearly presents the contrast in housing between that of the majority and that of the privileged few in Salvador, Bahia, a large urban center in Brazil. Classifying a country according to a single measure is often uninformative and is usually an oversimplification.
A further consideration is the variation of SES as measured by GNI PPP and urbanisation. Urbanisation and the rate of urbanisation are both related to SES, and may be a stronger risk factor than SES per se. The processes of urbanisation and modernisation are part of social and economic development and are associated with the adoption of a modern lifestyle in LMICs. Urban populations are growing rapidly throughout the world. Urbanisation has a profound effect on people's living conditions and health status and has been linked to asthma risk in Africa 23. Factors that contribute to this risk may include changes in diet and physical activity, infectious disease and microbial exposures, increased exposure to antibiotics and vaccines, allergen exposures, exposure to indoor irritants, the effects of industrial and motor vehicle pollution, and psychosocial stressors including violence 24. Large differences in asthma prevalence have been reported from urban and rural areas in Africa 25 and Asia 26, with a much higher prevalence of asthma reported in urban compared to rural populations. A question of practical importance is whether risk factors and mechanisms of asthma differ in high- and low-income countries, rural and urban settings.
THE WAY FORWARD
Understanding the forces that determine the burden of asthma, especially in developing countries, is important in the prioritisation of public health measures and resources. Poverty can also be a consequence of this chronic ailment. The determinants of chronic disease burden in general are by-products of globalisation, urbanisation, population ageing and general policy environment 27. A recent review of the social determinants of asthma in the USA draws attention to the fact that stress and violence are also emerging as significant risk factors 28. Poverty is a complex condition and it is not easy to unravel the effects of the various environmental and lifestyle factors involved in asthma causation, nor indeed the impact of this chronic disease upon the perpetuation of poverty. Considering that asthma is associated with demographic and socioeconomic indicators clustered by areas of residence not readily explained by traditional genetic paradigms or physical environmental exposures alone, a trans-disciplinary research approach with a shared conceptual framework that integrates analytical methods in multilevel, multi-method longitudinal studies has been proposed by the Asthma Coalition on Community, Environment and Social Stress Study (ACCESS) 29.
INACTION IS NOT AN OPTION
There are two great barriers to asthma prevention and control throughout the world. The first is a major gap in knowledge concerning causation and primary prevention. Asthma is a syndrome with multiple phenotypes related to complex gene–environment interactions. To address these gaps there is a need to scale up research on the topic worldwide. More funding, more collaboration and innovative approaches are urgently needed. Meanwhile, the outcomes of nationwide strategies based on plausible biological reasoning with simplification and standardisation of interventions and treatment such as those implemented in the Finnish Allergy Programme 26, should be closely considered for their potential application in LMICs. Lack of control of asthma is associated with avoidable reliance and expenditure on emergency care by underprivileged families and health systems that can hardly afford it 30. Simple interventions for management of asthma can control the disease, and reduce mortality, hospital admissions and costs 30–34, but they are not yet integrated to primary care policies or widely available. A crucial move towards feasibility and sustainability in LMICs would be the full integration of asthma management into primary healthcare routines, as reported in South Africa 35. Moreover, most subjects with asthma have concomitant rhinitis 36, which has been strongly associated with lack of control of asthma 37 and is usually neglected by the health systems in LMICs.
In May 2008, the World Health Assembly, with representatives from 193 countries, endorsed the 2008–2013 Action Plan of the Global Strategy for the Prevention and Control of Noncommunicable Diseases proposed by the World Health Organization 38. The Action Plan acknowledges four major groups of diseases that represent a leading threat to human health and development: cardiovascular diseases, cancer, chronic respiratory diseases and diabetes. Together, these cause 60% of all deaths globally, most of them in LMICs. All six objectives of the Action Plan 2008–2013 are highly relevant to the prevention and control of asthma, and two of them are directly related to the barriers mentioned above. Objective 2 of the Action Plan is to establish and strengthen national policies and plans for the prevention and control of noncommunicable diseases, and Objective 4 is to promote research for prevention and control of noncommunicable diseases. The Action Plan points to the need for partnerships between governmental and nongovernmental organisations in various sectors to address these objectives. The Action Plan has been adopted by the Global Alliance against chronic Respiratory Diseases (GARD) 39, 40, which has aligned its own action plan with this wider framework for disease control 38. Nongovernmental organisations such as the Global Initiative for Asthma (GINA) 41 and the Allergic Rhinitis and its Impact on Asthma (ARIA) initiative 42 have made, over many years, a substantial contribution to the fight against asthma by developing and disseminating evidence-based guidelines that have been adopted or adapted widely and form the basis for many national and regional guidelines. ARIA and GINA, together with many major professional organisations and parties from other sectors, and national departments of health are key participants in GARD. This global network has the potential to provide expertise, contagious enthusiasm and a united effort to support implementation strategies tailored to specific country needs, where requested by health authorities.
“Social justice is a matter of life or death. It affects the way people live, the likelihood of being unhealthy and to die prematurely” 43. However, effective health policies and practices can mitigate the consequences of social inequalities.
It is time to change the way asthma is handled in LMICs. Inaction is not an option! “You may say that I’m a dreamer, but I’m not the only one” (John Lennon) 44.
Support statement
A.A. Cruz is a member of the Executive Committees of the Global Initiative for Asthma (GINA) and the Allergic Rhinitis and its Impact on Asthma (ARIA), and of the Planning Group of the Global Alliance against chronic Respiratory Diseases (GARD). E.D. Bateman is the Chairman of GINA and a member of the GARD Executive Committee. J. Bousquet is the Chairman of GARD and ARIA.
Statement of interest
None declared.
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