Increasing Prevalence
Asia is the world's most populous continent, with a population of almost 4 billion people and many emerging economies. According to recent epidemiological data from ISAAC phase III, asthma and allergic rhinitis have increased in several areas, mostly in low-and middle-income countries.7,8 The prevalence of allergic diseases in Asia varies widely but was found to have increased (from 0.8% to 29.1% for asthma and from 5% to 45% for allergic rhinitis) as communities adopted modern lifestyles and became urbanized.
Time trends in the prevalence of asthma symptoms also showed different regional patterns, that is, a decrease in current wheezing in children aged 13 to 14 years in western Europe and an increase in wheezing children of the same age group in the Asia-Pacific region. Even within the Asian region, there was a wide variation among countries. The prevalence of asthma in Japan increased from 3.5% in 1982 to 4.6% in 19929 to 9.1% in 2006 (A. Akasawa, M.D., Ph.D., unpublished data, 2006) and was accompanied by an increase in allergic rhinitis of up to 32% (A. Akasawa, M.D., Ph.D., unpublished data, 2006). Similarly, 2 surveys performed in Taiwan using an identical method showed that the prevalence of childhood asthma had increased from 1.3% in 1974 to 5.07% in 1985.10 More recent ISAAC III data showed that in 13-and 15-yearold children in Taiwan, the overall cumulative and 12-month prevalences of wheezing and rhinitis in the younger children were 8.2% and 44.4%, respectively, and those in the older children were 6.9% and 42.2%, respectively.11 The percentage of children in Singapore who had experienced asthma at least once increased from 5.5% in 1967 to 13.7% in 1987 and to 20.7% in 1996. In Singaporean preschoolers aged 4 to 6 years, the cumulative and previous 12-month prevalences of wheezing were 27.5% and 16.0%, respectively. Asthma was reported by 11.7% of this group of children, and the current prevalence of rhinitis was 25.3%.
A field study conducted in four major cities in India with the use of a validated questionnaire showed the overall prevalence of asthma in 2006 to be 2.38%.12 In a recent study in rural Bangladesh, the prevalence of asthma in children was 16.1%.13 In contrast, in nonrural Lhasa, Tibet, the prevalences of current wheezing and diagnosed asthma were 0.8% and 1.1%, respectively.14 The prevalence of allergic rhinoconjunctivitis in Tibet was 5.2%. Even within the same country, the prevalence of asthma differed among various populations.7,8 Although overall regional data for adults are scant, between 1% and 10% of adults are estimated to have asthma, and between 10% and 32% are estimated to have allergic rhinitis.
Triggers And Risk Factors
Aeroallergens that trigger allergy and asthma vary from area to area in geographically diverse Asia. Although house-dust mites are the major triggering allergen in most of Asia, pollens, such as Japanese cedar pollen, are a major cause of allergic rhinitis in Japan. In a study of the prevalence of allergen sensitization among asthma patients in Thailand, house-dust mites (both Dermatophagoides species and Blomia tropicalis) were the most common sensitizing allergens in both pediatric and adult patients with asthma.15 Other important allergens, in order of priority, were cockroach and oil palm pollen. In contrast, less than 5% of patients were sensitive to other pollens and spores. Similarly, in a study of the sensitization profile of the general population in Southeast Asia to house-dust mites, subjects with rhinitis were most sensitive to B. tropicalis, followed by Dermatophagoides pteronyssinus (73% and 50%, respectively).16 Dual sensitization was common.
Although genetic factors are important in the manifestation of asthma and allergic rhinitis, the rapid increase in the prevalence of these disorders cannot be attributed to genetic factors alone. Changes in environmental factors also need to be taken into account. In a survey that compared the prevalence of asthma and atopic disorders in Chinese children aged 12 to 18 years in three Asian cities (Hong Kong, Kota Kinabalu, and San Bu, with Hong Kong being the most developed and westernized city), the prevalence of asthma and allergic disorders in children from Hong Kong was 2 to 6 times that in children from the other 2 cities.17 Allergic sensitization was a significant factor associated with asthma. The prevalence of atopy in Kota Kinabalu was high (64%), yet the prevalence of asthma was low (1.9%). In a cross-sectional prevalence analysis of wheezing, rhinitis, and eczema in Singaporean preschoolers aged 4 to 6 years, the main risk factors for current wheezing and self-reported asthma were family history of allergy, concurrent rhinoconjunctivitis, concurrent chronic flexural rash, and previous respiratory tract infection.18 In rural Bangladesh, risk factors associated with wheezing were pneumonia (at ages 0 to 12 months and 13 to 24 months), maternal asthma, paternal asthma, and maternal eczema.13
Despite extensive research on genetic, environmental, and lifestyle causes of asthma and on asthma risk factors--including pollution, tobacco smoke, diet, urban lifestyle, reduced early exposure to infections, and viral infections--no single factor has been identified as responsible for the marked geographic variation in or the increasing prevalence of asthma.
Morbidity and Mortality
Patients with asthma and allergic rhinitis have a reduced quality of life, and the burden of asthma, as assessed by disability-adjusted life-years, ranks 22nd among all diseases worldwide.19 Moreover, asthma in infancy often goes unrecognized and thus untreated.
The Asthma Insights and Reality in Asia-Pacific Study, which looked at patient perceptions of asthma management across Asia, concluded that patients experience frequent and unnecessary symptoms and exacerbations because of a lack of adequate asthma control.20 Indeed, 27% of adults and 37% of children with asthma in the Asia-Pacific region reported that this condition had resulted in an absence from school or work in the previous year, and 40% reported being hospitalized, visiting the emergency department or making unscheduled emergency visits to other health care facilities in the previous year. The severity of asthma varied, with Vietnam and China reporting the most patients with severe persistent symptoms. Work absence was highest in the Philippines (46.6%) and lowest in South Korea (7.5%). In another survey of parents of children with asthma from four Asian countries, most of the children (73%) had preexisting symptoms of allergic rhinitis at the time when asthma was diagnosed, and comorbid asthma and allergic rhinitis substantially affected quality of life and worsened asthma symptoms.21
Mortality associated with asthma varies from country to country and seems to be high in countries where access to essential drugs is low. The Global Initiative on Asthma estimates that approximately 250,000 persons die of asthma annually, and the death rate per 100,000 persons with asthma aged 5 to 34 years in highly populated China is greater than 10%.22 However, asthma can be controlled with optimal treatment. This has been proven in countries where an asthma management plan was implemented and the morbidity rate subsequently decreased.23
Socioeconomic Burden
The annual costs of treating asthma and allergic rhinitis--both direct costs (hospitalization, medications) and indirect costs (time lost from work, premature death)--are substantial and represent an even heavier burden in societies with emerging economies. The Asthma Insights and Reality in Asia-Pacific survey of urban centers in eight countries in the Asia-Pacific region showed that the annual per-patient direct costs ranged from US $108 in Malaysia to US $1010 in Hong Kong.24 Total per-patient costs, including productivity costs, ranged from US $184 in Vietnam to US $1189 in Hong Kong. Urgent care costs were 18% to 90% of the total per-patient direct costs. The economic burden in the Asia-Pacific region was higher than that in the United States in relation to the per capita gross domestic product (13% in the Asia-Pacific region compared with 2% in the United States) and per capita health care spending (300% in the Asia-Pacific region compared with 12% in the United States).24,25 Approximately US $20 billion are spent globally each year in relation to allergic rhinitis--a figure that includes the costs associated with medications, lost work productivity, and physician consultations. Approximately US $3 billion are spent in Japan alone.