a Institute of Diseases of the Chest and Hospital, Mohakhali, Dhaka-1212, Bangladesh.
b Institute of Child & Mother Health, Matuail, Dhaka-1362, Bangladesh.
c National Institute of Cancer Research & Hospital, Mohakhali, Dhaka-1212, Bangladesh.
d Bangladesh Institute of Child Health (Shishu Hospital), Sher-e-Bangla Nagar, Dhaka-1207, Bangladesh.
M Rashidul Hassan, Institute of Diseases of the Chest and Hospital, Mohakhali, Dhaka-1212, Bangladesh. E-mail: asmaasso{at}bttb.net.bd, mrhassan{at}bangla.net
Abstract
Background No population-based studies to determine the magnitude of the asthma problem have been carried out in Bangladesh. This study aimed to define the prevalence of asthma as well as to identify the risk factors of asthma in the general population of Bangladesh.
Methods A cross-sectional study was conducted from January 1999 to August 1999 on 5642 Bangladeshi people. Data were collected from randomly selected primary sampling units of 8 municipality blocks of 4 large metropolitan cities, 12 municipality blocks of 6 district towns and 12 villages of 6 districts chosen randomly from all 64 districts of the country. Face-to-face interviews were performed with the housewives or other guardians at the household level using a structured questionnaire.
Results The prevalence of asthma (wheeze in the last 12 months) was 6.9% (95% CI : 6.27.6). The prevalence of other asthma definitions were: ever wheeze (lifetime wheeze) 8.0% (95% CI : 7.38.7); perceived asthma (perception of having asthma) 7.6% (95% CI : 6.98.3); doctor diagnosed asthma (diagnosis of asthma by any category of doctor either qualified or unqualified) 4.4% (95% CI : 3.94.9). The prevalence of asthma in children (514 years) was higher than in adults (1544 years) (7.3% versus 5.3%; odds ratio [OR] = 1.41, 95% CI : 1.091.82). Asthma in children was found to be significantly higher in households with 3 people than in larger households (OR = 2.20, 95% CI : 1.243.20). The low-income group (OR = 1.41, 95% CI : 1.041.92) and illiterate group (OR = 1.51, 95% CI : 1.012.24) were more vulnerable to asthma attacks than the high-income group and more educated people, respectively.
Conclusions Asthma in Bangladesh appears to be a substantial public health problem: an estimated 7 million people including 4 million children suffer from asthma-related symptoms.
Keywords Asthma, wheeze, prevalence, population-based study, Bangladesh
Accepted 1 August 2001
Asthma is a substantial health problem among children and adults worldwide, with increasing prevalence rates in many countries.1 If 10% of children and 5% of adults have asthma, figures that are conservative for western countries1 but may be overestimates in some developing countries, the global burden of asthma is in the order of 130 million people. Mortality rates from asthma in western countries vary between one and five per 100 000, and result in some 60 000 deaths annually, many of which occur in young people and are preventable.2 International comparisons of prevalence and characteristics of asthma have been greatly facilitated by the completion of two major initiatives in asthma epidemiologythe European Commission Respiratory Health Study (ECRHS)3 and the International Study of Asthma and Allergies in Childhood (ISAAC).4 The first phase of ISAAC has been completed in 156 collaborating centres of 56 countries covering a population of 721 601 children.5 So far, only one study6 has been conducted to determine the prevalence of asthma in Bangladesh. It was conducted on children in a coastal region and showed the prevalence of asthma to be 11.8%. Since the nationwide prevalence of asthma was not known, this study was undertaken to determine the prevalence and associated factors of asthma and wheeze in Bangladesh in all age groups. It was conducted under the joint auspices of Asthma Association and The Chest and Heart Association of Bangladesh with collaboration from government health authorities, local medical practitioners and field workers.
Methods
This was a cross-sectional prevalence study, which quantified the distribution of asthma in the Bangladeshi population. This survey was conducted from January 1999 to August 1999.
Sampling and identification of the households
A multi-stage stratified random sampling design was followed. The whole country was stratified into three major strata: metropolitan, other urban and rural areas. The primary sampling unit (PSU) for the rural areas was village and that for urban areas was municipality block (mohalla). Data were collected from 14 metropolitan centres, 12 other urban centres and 12 rural centres. These centres were selected randomly. Twenty-five households for the metropolitan strata and 34 households for other urban and rural strata were selected randomly from each centre. On average, each household was considered to consist of five members. All members of the selected households were included in the survey.
Data collection procedure
Eight teams were formed for data collection. All members of the teams were physicians led by pulmonologists. In each household, face-to-face interviews were performed with the housewives or other available people using a pre-tested structured questionnaire (prepared on the basis of studies of ECRHS,3 ISAAC4 and Usherwood et al.7) to collect data about all members of the household. Information regarding the household was recorded on the first page of the questionnaire; separate questionnaires were used for each individual member of the household.
Definitions
Children were defined as those aged 514 years, adults as people aged 15 years. Children aged <5 years were excluded from the study. Assessment of the economic status of the families was based on questions on family income and expenditure in the month preceding the interview.
Surplus meant that income exceeded the expenditure. This is the affluent group having an approximate monthly income >Tk15 000 (>US$300) per month. Balance meant almost equal income and expenditure. This group comprises people with middle income having an approximate monthly income between Tk15 000 and
Tk3000 (
US$300 and
US$60) per month. Deficit indicated when expenditure exceeded the income. This is the poor group having an approximate monthly income <Tk3000 (<US$60) per month.
Wheeze was defined as the whistling sound arising from the chest and not from the nose or throat. Asthma prevalence was defined as the prevalence of recent wheeze (in last 12 months). Ever wheeze was wheeze any time in the past. Doctor diagnosed asthma was the asthma diagnosed by any category of doctor (either qualified or quack). Perceived asthma was the perception of having asthma in adults by themselves or in children by the parents. Night cough was defined as cough at night in the absence of any chest infection or heart disease in last 12 months. Night cough, waking was cough at night, which woke up the person, in the absence of any chest infection or heart disease in the last 12 months.
Statistical analysis
The prevalence of asthma and its different categories were estimated with exact binomial 95% CI. The 2 test or
2 test for trend were used for the difference between proportions. Age-standardized prevalence rates were calculated for the populations of metropolitan, other urban and rural areas using direct method of standardization. Adjustment was made using the Bangladeshi population of 1991 as reference.8 Unadjusted odds ratio (OR) with 95% CI based on observed prevalence were calculated to compare the patients with asthma to subjects without asthma. Multiple logistic regression analysis was applied to adjust for confounding among risk factors and to determine the most influential factors on asthma prevalence. The adjusted OR was calculated with a model that included age, sex, household size, economic status, schooling and smoking behaviour. All analyses were performed using SPSS version 7.5 for Windows.
Results
A total of 963 families were studied covering 5642 people. Table 1 shows the population characteristics of the studied population.
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Younger children of 59 years and adults of 3544 years were more likely to suffer from asthma than children aged 1014 years or younger adults, respectively (Tables 3 and 4). Small households (
3 members) were found to be more vulnerable (OR = 2.20, 95% CI : 1.243.20) to childhood asthma than larger households (
7 members). When considering all age groups, the deficit group (OR = 1.41, 95% CI : 1.041.92) as well as the illiterate group (OR = 1.51, 95% CI : 1.012.24) were found to be more vulnerable to asthma attacks than the surplus group and the more educated group, respectively.
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When considering only the oldest age group (45+ years), asthma was found to be more prevalent in illiterate people (OR = 2.69, 95% CI : 1.176.15) and populations living in other urban areas (OR = 1.69, 95% CI : 1.052.70).
Discussion
This population-based study confirms that the prevalence of asthma in Bangladesh is high. The prevalence among children was found to be higher than among adults. Children under 5 years were excluded from the study. It seems likely that respiratory viral infections have an important part to play in the production of wheeze in young children.9 Asthma is also more prevalent in people belonging to lower socioeconomic groups and adult populations of lower educational status.
This nationwide study provided the first opportunity to examine reported asthma symptoms in children and the adult population of Bangladesh. A standard methodology including stratified random sampling covering the whole country was followed. The instrument used in the study has been adapted from the ECRSH3, ISAAC4 and Usherwood7 questionnaires. Respiratory physicians were directly involved in the data collection process in the field.
Nonetheless, the study has a number of limitations. The first limitation of the study is the mode of ascertainment of asthma cases. The diagnosis was on the basis of reported symptoms ever and recent. This method of diagnosis could inflate the number of asthma cases due to similar presentation resulting from other diseases. On the other hand, the number of cases could be under-reported due to the long recall period. For population-based epidemiological studies, there is no satisfactory definition or gold standard diagnostic investigation for asthma. In common with most epidemiological studies on asthma, the symptoms suggestive of asthma and parental awareness were relied upon. In the stratification of economic status, there is no standard methodology for quick assessment in the community. We grouped the studied population on the basis of preceding month's income and expenditure into deficit, balanced and surplus groups. However, this method does not reflect the actual economic status of the family as perception of solvency varies among various strata of people.
The prevalence of childhood asthma (7.3%) is much lower than that of the developed countries like the UK (29%), Australia (30%), New Zealand (30%) and USA (21%) but similar to those of regional countries like Pakistan (8%) and India (7%).10 In general terms, higher prevalence rates have been found among children from westernized countries than in developing countries in Asia and Africa. These differences may be real or may reflect study methodology. The children of Bangladesh are very prone to infections like measles, tuberculosis, and helminthes. The prevalence of measles in children under 5 years and below 9 months was found to be 1.5% and 17.8%, respectively.11 The prevalence of tuberculosis in the Bangladeshi population was 0.5% of the total population.12 The prevalence of geohelminths in school children (age 514 years) by stool microscopy showed Ascaris lumbricoides in 69%, Trichuris trichura in 39% and Ankylostoma duodenale in 8%.13 The infections of tuberculosis and measles are protective against the development of asthma.1416 Helminthic infections also appear to protect against asthma.17
Asthma was found to be more prevalent in children aged 514 years (7.3%) than in the adults of 1544 years (5.3%) even after controlling for sex, household size, economic status and schooling. A similar finding was observed in Australia where asthma affects approximately one in five children and one in ten adults.18
Children in small households (3) were more vulnerable to asthma. The explanation might be that respiratory infections are less likely to occur in these less crowded households as compared to larger households where respiratory infections are more prevalent. It is proposed that certain viral infections early in life may be protective against the development of allergic disease.19 Declining family size, improvements in household amenities and higher standards of personal cleanliness have reduced the opportunity for cross infection in young families. This may have resulted in more widespread clinical expression of atopic disease.20 The prevalence of asthma was significantly higher in the less privileged social classes like the deficit and illiterate groups within the population. These findings are in concordance with the studies conducted in New York City where rates of hospitalization because of asthma were generally higher in poor, unemployed and less educated residents.21,22
Interestingly, our study shows that asthma is equally prevalent in metropolitan areas, in other urban areas and in rural areas. Though the city areas are highly polluted compared to rural and other areas, there is no definite basis that macroenvironmental factors such as climate and pollution are important determinants of regional variations of asthma severity. It is fashionable to ascribe the recent increase in the prevalence of asthma to atmospheric pollutants, such as nitrogen oxides, which have been implicated in the high prevalence of respiratory symptoms and asthma in western society. Pollution can undoubtedly trigger asthmatic attacks and be detrimental to lung function but the evidence regarding the role of pollutants in the development of asthma is much less convincing.23,24 These factors are possibly important in causing variations over a short period of time. A German study also supports this view, as no significant difference was shown in the lifetime prevalence of wheeze in two areas differing in pollution levels.25
The risk of asthma was greater among active smokers than non-smokers in this study. Cigarette smoking is a powerful risk factor for the development of chronic mucus hypersecretion and progressive airflow obstruction in middle and old age.26 The 4-year incidence of doctor diagnosed asthma among people aged 1039 years in Tucson, Arizona, was three times greater among smokers than among non-smokers at the start of the observation period.27
Further studies need to be done to look into the details of risk factors and protective elements for the development of asthma in Bangladesh.
KEY MESSAGES
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Acknowledgments
This study was funded by Asthma Association and The Chest and Heart Association of Bangladesh.
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