Paola Primatesta, Anne McMunn, Marion Brookes
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SUMMARY
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This chapter deals with asthma and asthma-related symptoms in adults (aged 16-74) and children (aged 2-15). Respiratory disease and asthma cause substantial illness and recent trends show an increase in the prevalence of asthma in the UK both in adults1 and children.2 It has been reported that the prevalence of diagnosed asthma and of asthma symptoms in children have increased at a rate of about 5% a year over the past 20 to 30 years.3 In Scotland a recent report showed that asthma was the second and third most frequent cause of consultation with general practitioners in boys and girls aged 5-15 and the most common cause of hospital admission in childhood.4
The definition of asthma and consequently the methods used to assess its prevalence have posed some problems in the past. Its customary definition is a syndrome characterised by wheezy dispnoea (shortness of breath), caused by a reversible widespread airways obstruction provoked by an increased level of responsiveness to a variety of stimuli. Given the reversibility of the obstruction the symptoms may vary in intensity and the level of discomfort between attacks may also show individual variations. Standardised protocols for assessing the prevalence of respiratory disease in epidemiological studies are mainly based on questionnaires which aim to measure the presence of respiratory symptoms. These were developed in the 1950s to identify people with emphysema and chronic bronchitis: the British Medical Research Council (MRC) questionnaire was the first standardised respiratory questionnaire, based on the presence of cough and sputum as predictors of chronic respiratory disability (chronic obstructive airways disease, COAD).5 Later versions included questions on wheezing and attacks of shortness of breath, which are symptoms frequently found in patients suffering from asthma. Wheezing is nevertheless a symptom also reported by COAD sufferers, and this may make it problematic to distinguish between the two conditions on the basis of questionnaires only. Criteria to validate asthma questionnaires relate responses to a clinical physiological investigation, or compare responses with a clinical diagnosis of asthma. Questions on wheezing as well as other indicators of asthma (such as breathlessness or diagnosis made by a doctor) have been validated against these criteria and have been used in large-scale epidemiological studies such as the International Study of Asthma and Allergies in Childhood, ISAAC6 and the European Community Respiratory Health Survey, ECRHS.7 These extensively used and well-validated questions have been used both in this survey and the Health Survey for England, as well as the MRC questions.
Adults and children aged 13 and over were interviewed personally, while for children aged 2-12 the relevant information was gathered from a parent or guardian. Informants were asked whether they had ever had wheezing or whistling in the chest. Those who reported ever having had wheezing or whistling in the chest were asked whether this was present without a cold or flu, whether they had ever experienced breathlessness with it, and if they had had an attack in the last twelve months. All informants were asked if they had ever been told by a doctor that they had asthma. Informants who reported having wheezed or whistled in the previous 12 months were asked about the frequency of attacks, the frequency of sleep disturbance and of speech limitation due to these symptoms and the extent to which the wheezing had interfered with their daily activities. Those informants who had ever wheezed or had doctor-diagnosed asthma and who had had an attack in the last five years were asked about sources of treatment or advice.
We report here on different respiratory symptoms: their presence, severity and impact on everyday life; use of health services; and, for adults only, variations in the prevalence of respiratory symptoms by region, degree of urbanisation, social class and cigarette smoking. The results are also compared with those obtained by combining data from the 1995 and 1996 Health Surveys for England.
The last section of this chapter reports on the distribution of serum total immunoglobulin E (IgE) levels and house dust mite specific IgE (HDM IgE) in children (comparing the results for Scotland and England). IgE is the class of antibodies responsible for the immediate type of immune response (that is for symptoms of allergy), and a raised serum concentration of IgE is found in people with an atopic predisposition. Atopy is defined as the production of specific IgE in response to common inhalant allergens in the environment, such as house dust mites, grass or domestic pets. The house dust mite, invisible to the naked eye, is found in dust throughout the house; it is the allergen to which most people with allergic disease are sensitised in Britain (80%, versus 40% sensitised to domestic pets). Being atopic is strongly associated with asthma and other allergic disease, although not everyone with asthma can be shown to be atopic when tested for specific IgE.
3.2 RESPIRATORY SYMPTOMS: PREVALENCE, SEVERITY AND IMPACT ON EVERYDAY LIFE
Wheezing at any time was reported by one quarter of all adults (25% of men and 24% of women) and of children aged 2-15 (27% of boys and 23% of girls). Around 15% of adults and children reported having wheezed in the last twelve months. Similar proportions reported they had ever had wheezing without a cold or had been breathless when wheezing.
The prevalence of wheezing in the past 12 months was higher in very young children (aged 2-6), in the age group 16-24 and then again in the age group 55-64 for women and mid to late 60s for men. The prevalence was higher in males than in females up to the mid 20s, then the differences between the two sexes were small up to the mid-late 60s. At that point rates in men had a second (higher) peak while the rate among women decreased.
Figure 3A
Figure 3A Prevalence of wheezing in the last 12 months, by age and sex (moving average of five age years)
Overall, a diagnosis of asthma made by a doctor was reported by 19% of boys and 16% of girls; 11% of men and 12% of women.
Prevalence rates for doctor-diagnosed asthma showed a different pattern to those for wheezing: they were high up to the early 20s then decreased rapidly in late 20s and remained stable throughout adult life. They were higher in boys and young men than their female counterparts up to the mid 20s. The decrease was nevertheless more marked in males than in females so that from the age group 25-34 women had higher prevalence than men.
Figure 3B
Figure 3B Prevalence of doctor-diagnosed asthma, by age and sex (moving average of five age years)
A diagnosis of asthma was reported by around 70% of children who reported wheezing in the last 12 months. The corresponding proportion in adults was only 45%, which did not change when ever wheezed was used instead of wheezing in the last 12 months. Of both children and adults who had ever had asthma, around 60% were symptomatic in the last 12 months. (Data not shown)
Among those adults who had experienced wheezing attacks in the past twelve months, 25% (28% of men and 22% of women) reported more than twelve attacks. Fifteen percent of men and 23% of women reported that their sleep had been disturbed once or more a week, while 45% of men and 55% of women said the symptoms interfered with their daily activities (16% and 22% respectively said they interfered 'quite a bit' or 'a lot'). Among children, 10% of boys and girls reported more than 12 attacks in the past 12 months, and 20% of boys and 25% of girls said that their sleep had been disturbed once or more a week. Fifty-five percent of boys and 65% of girls reported that the symptoms interfered with their daily activity: 16% and 18% respectively said they interfered 'quite a bit' or 'a lot'. In general, women reported more severe symptoms and higher levels of interference with daily life than men. Children had fewer attacks than adults in the past 12 months, but in general they seemed to have experienced more interference with daily activity than adults.
3.3 PREVALENCE OF WHEEZING AND DOCTOR-DIAGNOSED ASTHMA IN ADULTS
3.3.1 By region and degree of urbanisation
The age-standardised prevalence of wheezing in last 12 months was highest in the region of Lanarkshire, Ayrshire & Arran both for men (19.9%) and women (16.6%), and in Glasgow for women (17.4%). Lanarkshire, Ayrshire & Arran region also had a high prevalence of doctor diagnosed asthma in men (13.2%). In women Lothian & Fife had the highest prevalence of doctor-diagnosed asthma (13.9%). The lowest prevalence of wheezing among men was in Grampian & Tayside (12.3%), while Forth Valley, Argyll & Clyde had the lowest prevalence of doctor-diagnosed asthma for men (8.7%), as well as the lowest prevalence of both wheezing (12.0%) and asthma (9.4%) in women. Note, however, that few of the differences between regions were significant statistically.
The classification of areas as urban, suburban or rural was based on interviewers' observations at the address. In men neither wheezing in the last 12 months nor doctor-diagnosed asthma showed a tendency to be more common in those who lived in urban than in rural areas. In women, on the other hand, the age-standardised prevalence of wheezing was 18.9% in urban and 13.8% in rural areas; doctor-diagnosed asthma was also slightly more prevalent in urban (13.2%) than in rural areas (12.3%) though this difference was not statistically significant.
3.3.2 By social class
For both sexes, those in manual social classes had higher prevalence of wheezing in the last 12 months than those in non-manual classes. In men, the age-standardised prevalence increased from 8.2% in Social Class I to 21.2% in Social Class IV and 18.3% in Social Class V. In women, the prevalence more than doubled from 9.9% in Social Class I to 22.4% in Social Class V. Age-standardised prevalence of doctor-diagnosed asthma was also lowest in Social Class I both in men (8.8%) and in women (10.8%) but showed a less clear social class gradient.
3.3.3 By cigarette smoking status
The age-standardised prevalence of wheezing in the last 12 months clearly increased with the number of cigarettes smoked in both sexes. In men, the prevalence was 10.6% in non-smokers, and more than doubled (26.3%) in those who smoked more than 20 cigarettes a day. In women the differences were even larger, from 10.9% to 30.0%. However, the prevalence of doctor-diagnosed asthma did not seem to be affected by the informants' smoking status, the age-standardised prevalence remaining almost unchanged between smokers and non-smokers.
Others have noted that although smoking is an important risk factor for bronchial hyperreactivity (a feature of asthma) its association with asthma remains uncertain.3
3.3.4 By risk factors
Logistic regression was used to calculate the relative odds of reporting wheezing symptoms in the last twelve months and doctor-diagnosed asthma, separately for men and women, by smoking status (never regularly smoked, ex-regular smoker, less than 20 cigarettes a day, 20 or more cigarettes a day), social class and degree of urbanisation, adjusting for age group (16-24, 25-34, 35-44, 45-54, 55-64, 65-74).
After adjusting for age and other factors, smoking was significantly associated with wheezing symptoms in both sexes and the odds increased with the number of cigarettes smoked. The odds ratio (compared with non-smokers) was 1.96 for men who smoked less than 20 and 3.15 in those who smoked 20 or more cigarettes a day; and in women 1.87 and 3.39 respectively. Degree of urbanisation did not show a significant association in either sex. For social class the tendency was towards an increase in the odds of wheezing in manual social classes, but the differences were not significant after other factors such as smoking were taken into account. This would tend to suggest that the observed differences in social class could be explained partly by different levels of smoking in these groups.
When the analysis was repeated for doctor-diagnosed asthma, only cigarette smoking in women (but not in men) showed a significant association. The odds of reporting a diagnosis of asthma were about 1.3 in those who smoked less than 20 and 20 or more cigarettes a day compared with non-smokers.
3.4 USE OF HEALTH SERVICES BY ADULTS AND CHILDREN
Overall, over 23% of informants who had had an attack of wheezing or asthma in the 5 years before the interview reported they had not received advice or treatment about their condition (data not shown). Of those who had, around 95% of both adults and children mentioned they received treatment or advice from their GP. The second most frequently mentioned source was a consultant/specialist or another doctor at hospital outpatients for men (21%) and a nurse at the GP practice for women (21%). In children the nurse was also the second most frequent source, accessed by about a quarter. Differences in response between the sexes in sources of advice and treatment were very small.
3.5 COMPARISON BETWEEN SCOTLAND AND ENGLAND
3.5.1 Introduction
This section compares the prevalence of wheezing and asthma in Scotland with results from the 1995 and 1996 Health Surveys for England. Comparisons are with England as a whole and with Northern England, which included the two regions of Northern & Yorkshire and North West.
3.5.2 Prevalence of respiratory symptoms and doctor-diagnosed asthma in adults
The prevalence of ever wheezing and other wheezing symptoms was higher in England (and in Northern England) than in Scotland. This was true in both sexes and all age groups. On the other hand the prevalence of doctor-diagnosed asthma did not vary significantly between Scotland and England.
The prevalence of respiratory symptoms (phlegm, breathlessness and wheezing) as assessed by the MRC respiratory questionnaire was reported in the 1995 Scottish Health Survey. Then, comparisons with England showed that phlegm and breathlessness prevalence were both higher in Scotland while the prevalence of wheezing was very similar (around 20%) in Scotland and England. The MRC questionnaire was included again in the 1998 Scottish Survey, and cross-tabulating the two questions provide the following results:
| Wheezing | Wheezing (respiratory module) | ||
| (MRC respiratory questionnaire) | YES | NO | Total |
| YES | 73 % | 27% | 100% |
| NO | 3% | 97% | 100% |
While the correspondence for a negative answer was good (only 3% of those who said they did not have wheezing in the last 12 months when asked the MRC question answered affirmatively to a very similar question in the respiratory module), more than a quarter (27%) of those who said they had wheezing in the MRC question said they did not have wheezing when the question was asked in the respiratory module.
Overall, the prevalence of wheezing in the last 12 months as assessed by the MRC respiratory questionnaire was 19%, which is similar to the figure reported for Scotland in 1995, and for England both in 1994 and in 1998, when this instrument was used again (data not shown).
3.5.3 Prevalence of respiratory symptoms and doctor-diagnosed asthma in children
As with adults, the prevalence of asthma symptoms in children was lower in Scotland than in England. This is in agreement with some studies,8,9 though the ISAAC study found few geographical differences overall, but higher prevalence of wheezing in Scotland than in England.10
The differences observed in the prevalence of doctor-diagnosed asthma were mainly due to lower rates in Scotland among young children (aged 2-6), with the differences being very small in the older age groups.
In summary, according to the results, small geographical variations in prevalence of symptoms exist between Scotland and England, with a consistently lower prevalence of asthma symptoms in childhood and adulthood, of similar magnitude, in Scotland compared with England. On the other hand, the prevalence of reported doctor-diagnosed asthma did not show significant differences between Scotland and England.
The reported prevalences of asthma-related symptoms, hay fever and nasal allergies show wide geographical variations worldwide, and the distribution of atopy shows a similar distribution. This would support the importance of allergic reaction in the aetiology of the disease. This is nevertheless a complex disease and other factors, environmental and genetic, have also been shown to contribute to the development and severity of the disease.
3.6 SERUM IGE AND HOUSE DUST MITE SPECIFIC IGE IN CHILDREN
3.6.1 Measurement
IgE and house dust mite specific IgE were measured for children aged 11-15. Distributions were very skewed. For IgE the geometric mean was therefore calculated as well as the arithmetic mean (see Appendix E: Glossary). For house dust mite specific IgE, a result of ³0.4 kU/l is interpreted as abnormal; we report in section 3.6.3 on the proportions of children above and below this threshold.
Valid blood samples were obtained from 47% of children aged 11-15 (51% of boys and 43% of girls). Given that the proportion with valid samples is relatively low, some caution is needed when interpreting the results, as the subjects from whom the blood sample was obtained may not be entirely representative of the whole group of children aged 11-15.
3.6.2 Serum IgE
The geometric mean in all boys with a valid IgE sample was 63 kU/l; and in girls it was 55 kU/l. Geometric mean values were higher in boys than in girls in both age groups (11-12 and 13-15). Values for Scotland were lower than the corresponding ones in England (geometric mean in boys 73 kU/l, in girls 58 kU/l) and in Northern England. Table 3.15
Children's levels of IgE appeared to be higher in those with wheezing and doctor-diagnosed asthma than in those without, although small bases precluded reliable comparisons (data not shown).
3.6.3 House dust mite specific IgE
The proportion of children with HDM IgE ³0.4 kU/l was 45% in boys and 33% in girls. These proportions were higher than those observed in England and Northern England.
As already noted for total IgE, the proportion of children with HDM IgE ³0.4 kU/l tended to be higher among children with respiratory symptoms and asthma, but the bases were too small to allow meaningful comparisons (data not shown).