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The Scottish Health Survey: Volume 1: Main Report

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Chapter 8 Respiratory Health

8 RESPIRATORY HEALTH

Linsay Gray and Alastair Leyland

SUMMARY

  • Questions on respiratory symptoms and doctor-diagnosed asthma were asked in the 2008 and 2010 surveys. The data have been combined to provide more robust estimates.
  • Between 1998 and 2008/2010 the proportion of adults aged 16-74 that reported wheezing in the previous 12 months was very similar at 15%-16%. However, the prevalence of doctor-diagnosed asthma increased a little, from 11% in 1998, to 13% in 2003 and 14% in 2008/2010. The increase in asthma prevalence was more apparent among women than men.
  • 11% of adults aged 16-64 in 1995 and 1998 reported producing phlegm from their chest on most days for at least three months of the year, compared with 9% in 2008/2010.
  • The prevalence of attacks of wheezing or whistling in the chest, or shortness of breath at night, declined in adults aged 16-64 from 19% in 1995 and 1998, to 16% in 2008/2010.
  • 25% of adults aged 16-64 in 1995 reported breathlessness when walking on level ground or uphill, compared with 17% in 2008/2010. This decline was greater among women (from 30% to 20%) than men (from 20% to 13%).
  • In 2008/2010, 15% of adults aged 16 and over had wheezed in the last 12 months, and this did not vary by sex. Prevalence increased with age, from 11%-12% of those aged 16-34, to a peak of 20% in those aged 65-74, and was lower again for those aged 75 and over (16%).
  • 14% of adults aged 16 and over in 2008/2010 had doctor-diagnosed asthma. This was slightly but significantly lower in men (13%) than women (15%). Asthma prevalence declined steadily with age, from 22% of adults aged 16-24 to 9% of those aged 75 and over.
  • Men were more likely than women to report producing phlegm from their chest (12% versus 8%), whereas women were more likely than men to report breathlessness (25% versus 17%). Both phlegm production and breathlessness increased notably with age.
  • 30% of men and 34% of women who smoked 20 or more cigarettes per day had wheezed in the past 12 months compared with just 9% of men and women who have never smoked.
  • Asthma prevalence was higher among women who smoked 20 or more cigarettes a day (22%) than women who never smoked (13%), however the reverse was true for men.
  • The prevalence of wheezing in the last 12 months was generally highest among more socio-economically disadvantaged groups, for example, among adults in semi-routine and routine households, in the lowest income quintile households and the most deprived areas. The prevalence of doctor-diagnosed asthma was highest among adults in the lowest income households, and in the most deprived areas among women.
  • The proportion of children aged 2-15 that had wheezed in the last 12 months declined from 16% in 1998 to 13% in 2003 and 12% in 2008/2010. The prevalence of doctor-diagnosed asthma decreased from 18% in 1998 and 2003 to 14% in 2008/2010.
  • Patterns were different for boys and girls. Similar proportions of boys aged 2-15 experienced wheezing in the past 12 months in 1998 (16%) and 2008/2010 (14%), whereas the figures for girls declined from 14% in 1998 to 11% in 2003 and 10% in 2008/2010. The prevalence of doctor-diagnosed asthma in boys was similar in 1998 (19%) and 2003 (21%) but declined to 15% in 2008/2010. For girls, the corresponding figures were very similar each year (14%-16%).
  • In 2008/2010, among children aged 0-15, boys were more likely than girls to have ever wheezed (24% versus 19%). 14% of boys and 11% of girls aged 0-15 had been affected by wheezing during the last twelve months. 13% of children aged 0-15 had doctor-diagnosed asthma - the figures for boys (14%) and girls (12%) were not significantly different.
  • The prevalence of wheezing in the last 12 months was similar across all age groups, whereas doctor-diagnosed asthma increased clearly with age from 3% in children aged 0-1 and 8% of those aged 2-6, to 19% in children aged 11-15.
  • Children living in a household in which at least one person smoked indoors regularly were almost twice as likely to have doctor-diagnosed asthma as children living in households where no-one smoked indoors (19% versus 11%).
  • Regression analyses showed that girls were significantly less likely than boys to have wheezed in the previous 12 months. Area deprivation was significantly associated with wheezing in the last 12 months, but the pattern was not linear (prevalence was lowest among children in the middle deprivation quintile). Older children were more likely than younger children to have doctor-diagnosed asthma. Children who lived in homes where no-one smoked indoors were less likely to have asthma than children in with homes where at least one person smoked regularly indoors.

8.1 INTRODUCTION

Asthma is a common respiratory disease characterized by variable and recurring symptoms of breathlessness, wheezing, coughing and chest tightness. It is the most common chronic disease among children and considered to be of major public health importance. This year, the WHO estimated that 235 million people worldwide have asthma, [1] accounting for around 1 in every 250 deaths [2]. The UK has one of the world's highest rates of asthma in children [3] affecting one in 11 children. Currently 368,000 people in Scotland are receiving treatment for asthma - 1 in 14 adults and 1 in 13 children - of which 37,000 have severe asthma symptoms. [4] Comprehensive clinical guidelines on asthma management for adults and children in Scotland were developed by SIGN and the British Thoracic Society in 1999. These have been updated regularly since then, most recently in May 2011. [5] The guidelines include a wide range of topics on the diagnosis, monitoring and management of asthma, covering pharmacological, non-pharmacological and self-management in a variety of circumstances such as during adolescence or in pregnancy, labour and during breast-feeding.

Asthma causes substantial economic burden worldwide. The current number of disability-adjusted life years ( DALYs) lost due to asthma has been estimated to be around 15 million per year, accounting for an estimated 1% of all DALYs lost. This is similar to that for diabetes, cirrhosis of the liver, or schizophrenia, reflecting the high prevalence and severity of asthma. More than a quarter of asthmatics in Europe have days of reduced activity and use hospital services every year. [6] In 2004, asthma was estimated to account for at least 12.7 million work days lost in the UK each year. [7] It has been estimated that around 270,000 people (5% of the Scottish population) consult a general practitioner or practice nurse for asthma every two years. [8]

Triggers for asthma are wide ranging and include exposure to house dust mites, pollen, animals, specific foods, viral infections, moulds, fungi, environmental tobacco smoke [9] and air pollution. [10] Occupational exposures account for a substantial proportion of adult asthma incidence. [11]

Asthma affects all age groups, but often starts in childhood, [12] with around half of all people with asthma having experienced an attack by age 10 years. Asthma is more common in children than adults. Previous studies have shown that although prevalence is higher in boys than girls, in adults the prevalence is higher in women than men. [13] Those on low-incomes and children living in deprived areas experience more accident and emergency episodes, hospitalizations, and deaths due to asthma than the general population. [14]

Globally, the prevalence of asthma [15],[16] and wheeze [17] has increased among both adults and children in recent decades. Increases are predicted to continue, with an estimated additional 100 million persons with asthma worldwide by 2025. There are a number of factors associated with the increases in asthma prevalence, including: early life sensitization to aeroallergens, presence of atopic dermatitis or hayfever, maternal smoking during pregnancy and children's environmental exposure to tobacco smoke, exposure to air pollutants, [18] antibiotic treatment early in life and prematurity. [19] However none of these fully explain the rise in prevalence of asthma that had been seen in the UK. [20] In recent years, hospital admissions for asthma in Scotland have shown no clear trend. 8 Findings from the ISAAC surveys suggest that asthma in children in Scotland has become less common since the mid-1990s. [21]

Findings from the European Community Respiratory Health Survey ( ECRHS) [22] show that as well as asthma, the prevalence of general respiratory symptoms, wheezing, bronchial responsiveness and atopic sensitization [23] are each relatively high in the UK.

This chapter presents self-reported respiratory symptoms and doctor-diagnosed asthma in adults and children, by age and sex for the years 2008 and 2010 combined. Trends in symptoms and asthma diagnoses are shown by comparing the latest figures with the equivalent rates in 1998 and 2010; MRC Respiratory Symptom Questionnaire data for adults are additionally available from 1995. Differences by smoking status (adults), NS- SEC, household income, the Scottish Index of Multiple Deprivation and Scottish Government urban-rural classification (adults) are also presented. Children's symptoms are presented by their exposure to smoke in the home.

8.2 METHODS AND DEFINITIONS

The Scottish Health Survey has included a module about respiratory health in adults aged 16 and over in each round since its inception. The MRC Respiratory Symptom Questionnaire has been used throughout. This measures the presence or absence of common respiratory symptoms, such as phlegm production, breathlessness and wheezing or whistling in the chest. Breathlessness was classified as grade 1 if it occurred when hurrying on level ground or walking up a slight hill, or grade 2 (the more severe form), if it occurred when walking with other people of the same age on level ground.

In 1998 the survey questionnaire was expanded to include a section on asthma and asthma-related symptoms following the increased interest in rising rates of asthma worldwide. The asthma module comes largely from the questionnaire used in the ECRHS. 22 There is no 'gold standard' diagnosis for asthma but these questions and protocols have been standardised and extensively validated allowing legitimate comparisons of prevalence of asthma and other atopic conditions within and between countries. [24] The asthma module has also been asked of children aged 2-15 since 1998, and aged 0-1 since 2003.

From 2008 onwards, the Scottish Health Survey adopted a modular format designed to increase the number of topics covered in the 2008-11 period. As part of this, the asthma and respiratory symptoms questions were included only in the 2008 and 2010 surveys, with different topics included in their place in 2009 and 2011. To increase the number of cases available for the analysis, the 2008 and 2010 data have been combined.

The nurse visit includes an objective measure of adult lung function, measured via spirometry. Only a sub-sample of participants is included in the nurse visit. The 2011 report will include a comprehensive overview of the lung function data, drawing on the larger sample size from the pooled 2008-2011 data.

8.3 TRENDS IN ADULT RESPIRATORY SYMPTOMS

This section focuses on trends. The next section describes adults' respiratory symptoms in 2008/2010 in greater detail. Table 8.1 shows the prevalence of respiratory symptoms and asthma based on the questions within the asthma module, by age and sex in 1998, 2003 and 2008/2010. Table 8.2 presents the prevalence of phlegm production, breathlessness and wheezing as assessed by the MRC respiratory questionnaire in 1995, 1998, 2003 and 2008/2010.

Changes to the sample composition since 1995 mean that the overall figures presented for adults from 1995 are for those aged 16-64, and from 1998 for those aged 16-74. The figures for all adults aged 16 and over are also shown for 2003 and 2008/2010.

8.3.1 Wheezing and asthma

There is no clear trend in the prevalence of respiratory symptoms presented in Table 8.1 over the 1998 to 2008/2010 period. The proportion of adults aged 16-74 that reported wheezing in the previous 12 months was very similar in all years (15%-16%), whereas the prevalence of doctor-diagnosed asthma was a little lower in 1998 (11%) compared with 2003 (13%) and 2008/2010 (14%). The separate figures for men and women followed the same pattern as all adults for wheezing in the past 12 months. However, the overall increase in asthma prevalence was more apparent among women, who saw a linear increase from 12% in 1998 to 14% in 2003, and then up to 16% in 2008/2010.

Table 8.1 also shows figures for men and women for some other respiratory symptoms. For the whole period, around a quarter of men (24%-27%) and women (24%-26%) aged 16-74 reported a history of ever wheezing or whistling. Prevalence of wheezing symptoms (wheezing without a cold and instances of being breathless when wheezing) was generally stable between 1998 and 2008/2010.

The total figures for adults aged 16 and over in 2003 and 2008/2010 were in almost all cases identical to those for adults aged 16-74.

Table 8.1

8.3.2 MRC respiratory questionnaire symptoms

The figures in Table 8.2 follow some of the patterns in Table 8.1. A slightly lower proportion of adults aged 16-64 reported producing phlegm from their chest on most days for at least three months of the year in 2008/2010 (9%) compared with 1995 and 1998 (11%). The reduction in men (from 13% in 1995 and 1998 to 10% in 2008/2010) was statistically significant, but the smaller decline in women (from 9% to 7%, respectively) was not. The prevalence of attacks of wheezing or whistling in the chest, or shortness of breath at night, declined in adults aged 16-64 from 19% in 1995 and 1998, to 16% in 2008/2010, with similar patterns evident for men and women. The combined prevalence of grade 1 and grade 2 breathlessness in adults aged 16-64 declined each year from 25% in 1995 to 17% in 2008/2010. The decline between 1995 and 2008/2010 was greater among women (from 30% to 20%) than men (from 20% to 13%). The overall decline was entirely due to a halving in the prevalence of grade 1 breathlessness (from 17% to 8%, respectively). The more severe form, grade 2, was unchanged at 8% each year. This pattern was the same for men and women. Table 8.2

8.4 ADULT RESPIRATORY SYMPTOMS IN 2008/2010

8.4.1 Wheezing by age and sex

This section looks at the results for respiratory symptoms and asthma in adults aged 16 and over for 2008 and 2010 combined, shown in Table 8.1. Overall, one in four adults - 24% of men and 25% of women - had a history of wheezing at any time in their lives. Lifetime wheezing prevalence did not vary significantly by sex, or by age for either sex.

Prevalence of wheezing symptoms ( i.e. wheezing without a cold and being breathless when wheezing) was generally similar in both sexes (15% to 17%) and at all ages. Confining attention to the last 12 months, 15% of adults had wheezed during this time and this did not vary by sex. Prevalence increased with age, from 11%-12% of those aged 16-34, to a peak of 20% in those aged 65-74, and was lower again for those aged 75 and over (16%). Table 8.1

8.4.2 Doctor-diagnosed asthma by age and sex

14% of adults had doctor-diagnosed asthma; this was slightly but significantly lower in men (13%) compared with women (15%). As Figure 8A illustrates, for both sexes, the youngest age group had the highest prevalence of asthma: 22% of adults aged 16-24 reported a diagnosis of asthma, this then declined fairly steadily with age to 9% of those aged 75 and over. Figure 8A, Table 8.1

Figure 8A

8.4.3 Phlegm production and breathlessness by age and sex

This section looks at the phlegm production and breathlessness results in adults aged 16 and over for 2008 and 2010 combined, shown in Table 8.2. Men were more likely than women to report producing phlegm from their chest (12% versus 8%), whereas women were more likely than men to report breathlessness (25% versus 17%). Both phlegm production and breathlessness increased with age. Figure 8B shows that the prevalence of breathlessness was over 40% from the age of 65 in women, and 75 in men. Figure 8B, Table 8.2

Figure 8B

8.5ADULT RESPIRATORY SYMPTOMS BY SMOKING STATUS

To ensure that the comparisons presented in this section are not confounded by the different age profiles of the sub-groups, the data have been age-standardised (age-standardisation is also described in the Glossary). Only age-standardised figures are reported in the tables.

Wheezing in the last 12 months was significantly associated with cigarette smoking status. Wheezing prevalence was just 9% in men who have never smoked and was three times as high (30%) in those who smoked 20 or more cigarettes per day. The associations were similar in women, with wheezing prevalence of 9% in never smokers compared with 34% in those smoking 20 or more cigarettes per day. For both men and women, prevalence among smokers was higher for those smoking 20 or more a day than for those smoking less than this.

On the other hand, the prevalence of doctor-diagnosed asthma was lowest in men who smoke 20 or more cigarettes per day (6%) compared with 13%-14% in all other groups. This may be due to people with asthma being advised to stop smoking, or it could be due to undiagnosed asthma among smokers. However, the opposite was true among women (22% of those who smoked 20 or more cigarettes a day had asthma compared with 13%-17% of those who smoked less than this amount, or were ex or never smokers). Although the 16 percentage point difference between the asthma prevalence in men and women smokers of 20 or more per day was significant, the sample size for this group was small and the previous figures, in 2003, did not show such a pronounced pattern. [25] Other sources of evidence would be needed before firm conclusions can be drawn about sex differences in the prevalence of asthma among smokers. Table 8.3

8.6 ADULT RESPIRATORY SYMPTOMS BY SOCIO-DEMOGRAPHIC FACTORS

Tables 8.4 to 8.6 present the prevalence of respiratory symptoms and doctor-diagnosed asthma among men and women, by socio-economic classification ( NS- SEC of the household reference person), equivalised household income and the Scottish Index of Multiple Deprivation (descriptions of each of these measures are available in the Glossary at the end of this volume).

The prevalence of respiratory symptoms and doctor-diagnosed asthma are also given by the Scottish Government 6-fold urban rural classification. This classification uses settlement sizes and accessibility measures based on drive time data, to classify areas of Scotland into six categories ranging from large urban to remote rural areas. [26]

As for respiratory symptoms by current smoking status, the data have been age-standardised to ensure that the comparisons presented in this section are not confounded by the different age profiles of the sub-groups (age-standardisation is described in the Glossary). Only age-standardised figures are reported in the tables.

8.6.1 Socio-economic classification ( NS- SEC)

There was a significant association between NS- SEC and the prevalence of wheezing in the last 12 months. The highest prevalence was found among adults in semi-routine and routine households for both men and women. Among men, 19% of those in semi-routine and routine households had wheezed in the past 12 months compared with 10% of those in managerial and professional households, 9% in intermediate households and 14% in the remaining two household types. Among women, prevalence was 21% among those in semi-routine and routine households, compared with 12% in professional and managerial households, 10% in small employer households, and 15%-17%, in the other two groups.

For doctor-diagnosed asthma, there was no association with NS- SEC in either men or women. Table 8.4

8.6.2 Equivalised household income

The prevalence of wheezing in the last 12 months generally increased as equivalised income decreased for both sexes. The prevalence of wheezing in the highest income quintile was 8% for men and 11% for women compared with 24% for men and 26% for women in the lowest quintile, with broadly stepwise increases over the income range (see Figure 8C).

Men and women in the lowest income quintile households had the highest prevalence of doctor-diagnosed asthma. 17% of men and 21% of women in the lowest income quintile households had asthma compared with 12% to 13% of men, and 13% to 15% of women, in the other groups. Figure 8C, Table 8.5

Figure 8C

8.6.3 Scottish Index of Multiple Deprivation ( SIMD) and Scottish Government urban-rural classification

Wheezing in the last 12 months was significantly associated with SIMD for both sexes, with lowest prevalence in the least deprived quintile. Wheezing prevalence was 8% among men in the least deprived areas, compared with 15% and 11% in the two next quintiles, and 18% and 21% in the two most deprived quintiles. The pattern among women was more straightforward, with increasing wheezing prevalence as deprivation increased, from 11% to 23% between the least and most deprived areas.

Doctor-diagnosed asthma prevalence was lowest in the least deprived areas for men and highest in the most deprived areas for women but there were no clear linear patterns. Table 8.6

The prevalence of wheezing in the past 12 months was higher in men and women in the 15% most deprived areas than the rest of Scotland (21% versus 13% for men, 24% versus 14% for women). Doctor-diagnosed asthma prevalence was not significantly different between the 15% most deprived areas and the rest of Scotland for men or women.

Table 8.7 presents respiratory symptoms by urban-rural classification. No clear association was observed between wheezing in the past 12 months, or rates of doctor-diagnosed asthma, and type of area for men or women. In most cases the prevalence of symptoms was very similar in the most urban and most rural areas, with some variations in between but no obvious patterns. Table 8.7

8.7 FACTORS ASSOCIATED WITH ADULT RESPIRATORY SYMPTOMS

Logistic regression was used to examine the factors associated with wheezing symptoms in the last twelve months and doctor-diagnosed asthma, separately for men and women. The variables included in the analysis were: age group, smoking status (never smoked, ex-smoker, smokes less than 20 cigarettes a day, smokes 20 or more cigarettes a day), whether non-smokers were exposed to second-hand smoke, the number of people smoking in the home (none, one or more), highest educational qualification, NS- SEC of the household reference person, equivalised household income, SIMD and area type (urban/rural). By simultaneously controlling for a number of factors, the independent effect each factor has on the variable of interest can be established. Logistic regression compares the odds of a reference category (shown in the table with a value of 1.00) with that of the other categories. In this example, an odds ratio of greater than one indicates that the group in question is more likely to report wheezing symptoms, or have doctor-diagnosed asthma, than is the chosen reference category; an odds ratio of less than one means they are less likely. For more information about logistic regression models and how to interpret their results see the glossary at the end of this volume.

Table 8.8 presents the results from the logistic regression analysis including all variables that were significant for men and/or women. Second-hand smoke exposure, number of people smoking at home, highest educational qualification, NS- SEC and area type were not significant in either analysis, while smoking status was not significant for the asthma analysis, therefore these are absent from the table.

8.7.1 Wheezing in the past 12 months

Age was significantly associated with wheezing symptoms in men but not women. The odds of wheezing were significantly higher among men aged 45 and over compared with those aged 16-24 (odds ratios of 1.99 to 2.63). Equivalised household income was significantly associated with wheezing in men and women: the odds tended to increase as income decreased, with significantly higher odds for men in the 4 th quintile (odds ratio of 1.75) and men and women in the 5 th quintile (odds ratios of 2.46 and 2.09, respectively) compared with those in the 1 st quintile. Area deprivation was also significantly associated with wheezing symptoms for men: the odds were 1.89 and 2.09 times higher among the two most deprived area quintiles compared with the least deprived areas. Smoking was associated with wheezing symptoms in both sexes, with the odds increasing as the number of cigarettes smoked increased. Among women, the odds of wheezing were 1.62 times higher for ex-smokers compared with those who have never smoked, 3.02 times higher for those who currently smoke fewer than 20 cigarettes per day, and 3.90 times higher for those who currently smoke 20 or more cigarettes per day. The equivalent odds ratios for men were 1.39, 2.84, and 3.32, respectively, with significant effects for the latter two. Table 8.8

8.7.2 Doctor-diagnosed asthma

When the analysis was repeated for doctor-diagnosed asthma only age showed a significant association for both sexes, while income and area deprivation were also significant for women. The fact that smoking had an independent significant association with wheezing, but not with asthma, confirmed the findings discussed above in Section 8.5. It is possible that smoking habits change following a diagnosis of asthma, or that asthma is undiagnosed in some smokers.

The odds of reporting an asthma diagnosis generally decreased with age. The odds of men and women aged 45 and over reporting doctor-diagnosed asthma were significantly lower compared with the youngest age group (odds ratios of 0.31 to 0.55). Among women, there was a marginally significant overall association with income, although none of the groups had significantly higher odds than the highest income group. Re-running the analysis with the lowest income group as the reference category showed that the odds of doctor-diagnosed asthma were significantly lower for women in the 4 th and 3 rd income quintiles compared with the lowest (data not shown). The pattern for deprivation reflected that seen in Table 8.6, with the odds of doctor-diagnosed significantly lower among women in the 4 th least deprived quintile compared with the least deprived. Table 8.8

8.8 TRENDS IN CHILDREN'S RESPIRATORY SYMPTOMS

This section presents respiratory symptom and asthma figures for the 1998, 2003 and 2008/2010 surveys for boys and girls aged 2-15 ( Table 8.9). The figures for those aged 0-15 in 2003 and 2008/2010 are also shown. Figures for two of the measures (wheezing in the past 12 months and asthma diagnosis) in the three periods are also shown for boys and girls combined.

8.8.1 Trends in children aged 2-15, 1998-2008/2010

The proportion of children aged 2-15 that had wheezed in the last 12 months declined from 16% in 1998 to 13% in 2003 and 12% in 2008/2010. The figures for doctor-diagnosed asthma decreased from 18% in 1998 and 2003 to 14% in 2008/2010.

The separate patterns for boys and girls were a little different to those for all children. Similar proportions of boys aged 2-15 experienced wheezing in the past 12 months in 1998 and 2003 (16%) and 2008/2010 (14%), whereas the figures for girls declined from 14% in 1998 to 11% in 2003 and 10% in 2008/2010. The prevalence of doctor-diagnosed asthma in boys was similar in 1998 (19%) and 2003 (21%) but declined to 15% in 2008/2010. For girls, the corresponding figures were very similar each year and did not vary significantly (16% in 1998, 14% in both 2003 and 2008/2010).

Table 8.9 also includes figures for some other respiratory symptoms. The prevalence of ever having wheezed followed a similar pattern to that for wheezing in the last 12 months. It fluctuated among boys aged 2-15 over the years with no obvious pattern (27% in 1998, 30% in 2003, and 25% in 2008/2010). For girls the prevalence of ever having wheezed declined from 23% in 1998, to 21% in 2003 and 20% in 2008/2010. Associated symptoms ( i.e. wheezing without a cold and being breathless when wheezing) similarly fluctuated among boys but were more stable among girls.

8.8.2 Trends in children aged 0-15, 2003-2008/2010

The 2003 and 2008/2010 figures for children aged 0-15 were very similar to those for children aged 2-15. For example, 14% of children aged 0-15 in 2003, and 12% in 2008/2010, had wheezed in the last 12 months. 16% and 13%, respectively, had doctor-diagnosed asthma.

Between 2003 and 2008/2010, 12 month wheezing prevalence was broadly stable for both boys (16% and 14%, respectively) and girls (12% and 11%, respectively) aged 0-15 years. Asthma prevalence was stable in girls (12%) but declined for boys (from 20% to 14%) in this period.

The proportion of girls aged 0-15 that had ever wheezed was similar in 2003 (20%) and 2008/2010 (19%), but decreased for boys from 29% in 2003 to 24% in 2008/2010. Associated respiratory symptoms ( e.g. non-cold related wheezing, and breathlessness) generally followed similar patterns .Table 8.9

8.9 CHILDREN'S RESPIRATORY SYMPTOMS IN 2008/2010

Table 8.9 shows that boys aged 0-15 in 2010 were more likely than girls to have ever wheezed (24% versus 19%), a statistically significant difference. Fewer children had been affected by wheezing during the last twelve months (14% of boys and 11% of girls). Similarly, reported wheezing without a cold or being breathless when wheezing, was more common in boys than girls (14% versus 11%). The higher prevalence of symptoms in boys than girls was evident for all age groups for most symptoms. As Figure 8D illustrates, with the exception of wheezing in the past 12 months, the prevalence of the other wheezing symptoms was generally higher in children aged 7-15 than 0-6.

13% of children aged 0-15 had doctor-diagnosed asthma. The small difference between boys (14%) and girls (12%) was not statistically significant. The prevalence of doctor-diagnosed asthma increased clearly with age from 3% in children aged 0-1 and 8% of those aged 2-6, to 19% in children aged 11-15.

Figure 8D, Table 8.9

Figure 8D

8.10 CHILDREN'S RESPIRATORY SYMPTOMSBY EXPOSURE TO SECOND-HAND SMOKE AT HOME

Table 8.10 presents the proportions of children who had wheezed in the last 12 months, or had doctor-diagnosed asthma, by their exposure to smoking in the home. Participants were asked how many people regularly smoked inside their home, including visitors and household members. [27] There was no association between children's wheezing in the previous year and whether anyone smoked inside their home. In contrast, children living in a household in which at least one person smoked indoors were almost twice as likely to have doctor-diagnosed asthma as children living in households where no-one smoked indoors (19% versus 11%). Although the sample sizes for the different age groups are relatively small, it appears that the association between asthma and exposure to second-hand smoke in the home is particularly strong for children aged 0-6 years. 15% of children aged 0-6 exposed to smoke indoors had asthma versus 4% of those not exposed, compared with 22% and 16%, respectively of those aged 7-15. Table 8.10

8.11 CHILDREN'S RESPIRATORY SYMPTOMS BY SOCIO-DEMOGRAPHIC FACTORS

Tables 8.11 to 8.13 present the prevalence of wheezing in the past 12 months, and doctor-diagnosed asthma, among boys, girls and all children, by NS- SEC of household reference person, equivalised household income and SIMD. Unlike the equivalent analysis for adults, the sample is not big enough to permit a robust comparison of children living in the 15% most deprived areas and the rest of Scotland, or the different urban-rural categories. Similarly, a collapsed version of NS- SEC has been used which combines some of the categories.

8.11.1 NS- SEC

The prevalence of wheezing in the last 12 months was higher among children in lower supervisory and technical, semi-routine and routine households (14%) than children in professional and managerial households (10%). The difference was greater for boys than girls.

For doctor-diagnosed asthma, the differences between children in the three household types were not significant. Table 8.11

8.11.2 Equivalised household income

The prevalence of wheezing in the past 12 months was highest in children in the lowest income quintile households (16%) compared with the highest two quintiles (10%). As with NS- SEC, this pattern was more apparent in boys than girls.

The higher prevalence of doctor-diagnosed asthma among children in the lowest income quintile (17% versus 11%-13% in the other four quintiles) was not statistically significant. However, the difference between boys in the lowest and highest income households (21% and 10%, respectively) was significant. The sample sizes for these groups are relatively small so the difference between them might not be as great as the two-fold size suggested here. Table 8.12

8.11.3 SIMD

There was a significant association between area deprivation and the prevalence of wheezing in the past 12 months and doctor-diagnosed asthma. However, the pattern was not straightforward. Children in the middle deprivation quintile were the least likely to have experienced these respiratory symptoms while those in the most deprived quintile were the most likely. This pattern was true for wheezing prevalence in both boys and girls, but was only evident for asthma among boys.

Table 8.13

8.12 FACTORS ASSOCIATED WITH CHILDREN'S RESPIRATORY SYMPTOMS

Logistic regression was used to examine the factors associated with wheezing symptoms in the last 12 months and doctor-diagnosed asthma in children, by age, sex, whether anyone smoked inside the home, number of siblings, NS- SEC, equivalised household income, SIMD, and area type (urban/rural). No parental variables ( e.g. indicators of whether the children's parents smoke, or themselves have respiratory symptoms) were considered for these analyses as the sample size is not sufficient to accommodate this.

Table 8.14 presents the results of the logistic regression analyses including all the risk factors that were significant for children. Number of siblings, NS- SEC, equivalised household income and area type were not significant in either analysis. Age and whether anyone smoked inside the home were not significant for the wheezing analysis, while sex and SIMD were not significant for the asthma analysis, therefore these are absent from the tables.

8.12.1 Wheezing in the past 12 months

Girls were less likely than boys to have wheezed in the previous 12 months (odds ratio of 0.74). Area deprivation was significantly associated with wheezing. However, as Table 8.14 illustrates, the differences between children in the least deprived quintile (the reference category) and children in the other groups were not significant, hence the confidence intervals for the odds ratios all include the value 1. Table 8.14

8.12.2 Doctor-diagnosed asthma

The odds of children aged 7-15 having doctor-diagnosed asthma were 3.10 times higher than for those aged 0-6. Compared with children who lived in homes where no-one smoked indoors, the odds of doctor-diagnosed asthma among those living in accommodation where at least one person smoked indoors were 1.92 times higher. Table 8.14