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4102.0 - Australian Social Trends, 1999  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 24/06/1999   
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Contents >> Health >> Mortality & Morbidity: Asthma

Mortality & Morbidity: Asthma

In 1995, it was estimated that over two million Australians (11% of the total population) had asthma. Between 1989-90 and 1995, self-reported asthma prevalence increased by about one third.

The risk of dying from asthma is low and continues to decline in Australia. However, prevalence of asthma appears to be increasing and is a cause of concern for health authorities and the general population because of the personal, social and economic costs associated with the disease.

Between the 1989-90 and the 1995 National Health Surveys, the proportion of the population reporting asthma (as a recent illness and/or as a long term condition) increased by about one third. The increase in self-reported asthma prevalence was greater among adults (41%) than among children (17%) and, for both children and adults, the increase was greater among females than males. Improvements in identification and treatment of asthma, increased public awareness of the condition, and small differences in survey methodology between 1989-90 and 1995 may all have contributed to greater reporting of asthma in 1995. However, it is not possible to measure how much of the increase in reporting is due to these factors and how much reflects actual increases in asthma prevalence.

The 1995 National Health Survey (NHS) estimated that over 2 million Australians (11% of the total population) had asthma. Prevalence rates were highest among 5-14 year olds (21% among boys and 17% among girls). Asthma prevalence was also relatively high among 15-24 year olds, with 16% of females and 14% of males in this age group reporting that they had asthma in 1995. Up to 15 years of age, asthma was more common among boys than girls. In older age groups, however, the condition was generally more common among women than among men, with prevalence rates converging for persons aged 75 and over.


Asthma

Asthma is a disease characterised by airway-wall inflammation.1 It is a chronic (long-term) condition which may be punctuated with acute (short-term) episodes at varying intervals and varying degrees of severity. Severe acute attacks can result in death.

In the short term, asthma causes bronchial hyper-responsiveness, variable airway narrowing and mucus production, giving rise to the typical symptoms of asthma - wheeze, dyspnoea (difficult or painful breathing), and cough. Over many years, persistent airway inflammation may cause fixed airway narrowing, with a reduced response to broncho-dilating agents.1

The underlying causes of asthma are not known, but the combination of genetic factors and exposure to allergens (e.g. house dust mite, animal dander, moulds) or chemicals (e.g. formaldehyde, PVC, latex) results in sensitisation and airway inflammation.2 Acute episodes may be triggered by exercise, some food additives, some medications, and a range of common irritants such as environmental tobacco smoke (passive smoking), pressurised aerosols, soap powders, solvents and airconditioning.1

Self-reported prevalence of asthma

Statistics on self-reported prevalence of asthma in Australia were compiled by the ABS using information collected from households in two National Health Surveys - conducted in 1989-90 and 1995. Where possible, a personal interview was conducted with each adult. A parent or guardian was asked to provide information about children in the household. Respondents may have reported asthma as a recent illness, a long-term condition, or both.

Recent illness - respondents may have reported asthma as the reason for taking one or more specified health-related actions during the two weeks before interview (e.g. doctor consultation, medication use, time away from work/school) or as an illness episode in the two-week reference period for which no specified action was taken.

Long-term condition - respondents also had the opportunity to report having asthma as a long-term health condition (i.e. a condition which has lasted, or is likely to last, for six months or more) regardless of whether they had experienced a recent episode or taken any recent health-related action for their asthma.

Reported information on medical conditions was not medically verified, and was not necessarily based on diagnosis by a medical practitioner. Self-reported information on medical conditions may differ from information which might be obtained from other sources.

SELF-REPORTED PREVALENCE OF ASTHMA AMONG CHILDREN AND ADULTS

Number
Prevalence rates

1995
1995
1989-90
Increase 1989-90
to 1995
'000
%
%
%

Children (0-14 years)
632.6
16.3
13.9
17.3
    Boys
363.4
18.3
16.3
12.3
    Girls
269.2
14.3
11.4
25.4
Adults (15 years and over)
1,408.8
9.9
7.0
41.4
    Men
618.2
8.8
6.4
37.5
    Women
790.6
11.0
7.5
46.7
Total
2,041.4
11.3
8.5
32.9
    Males
981.6
10.9
8.7
25.3
    Females
1,059.8
11.7
8.3
41.0

Source: 1995 National Health Survey: Asthma and Other Respiratory Conditions, Australia (cat. no. 4373.0); and unpublished data, 1989-90 National Health Survey.


SELF-REPORTED ASTHMA PREVALENCE RATES BY AGE, 1995
Source: 1995 National Health Survey: Asthma and Other Respiratory Conditions, Australia (cat. no. 4373.0)


Smoking and asthma
A recent report3 by the National Health and Medical Research Council (NHMRC) found that passive smoking is firmly linked, as a likely causal factor, to a range of health problems including lower respiratory tract disease and asthma in children. The NHMRC estimates that children exposed to environmental tobacco smoke are about 1.4 times as likely to suffer from asthma as children who are not exposed, and that around 8% of childhood asthma cases are attributable to passive smoking.

The 1995 NHS found that prevalence of asthma was higher (about 4 percentage points) among young children living in households with one or more smokers than in households with no smokers present. Among 10-14 year olds, however, prevalence of asthma was lower in households with smokers present. The Survey did not collect any information about whether children had ever been exposed to household smoking in the past, or whether they were currently exposed to smoking outside the home.

The 1995 NHS also found that asthma prevalence was higher among women who were either current smokers or ex-smokers than among those who had never smoked. For men, however, the relationship between asthma and smoking status appeared to be much weaker.

SMOKING AND SELF-REPORTED ASTHMA PREVALENCE RATES, 1995
Children(a)
Adults(b)

(a) Aged under 15 years.
(b) Aged 18 years and over. Prevalence rates have been age standardised to the total population (aged 18 years and over) at 30 June 1995.

Source: 1995 National Health Survey: Asthma and other Respiratory Conditions, Australia (cat. no. 4373.0).


Treatment of asthma
Asthma can be controlled with preventive medications and strategies to reduce airway inflammation.1 In 1995, an estimated 1.1 million people (55% of all people with asthma) reported using medication for their asthma during the two weeks before interview. The proportion using medication increased steadily with age, from 49% of 0-14 year olds to 68% of those aged 65 years and over.

While children were less likely than other age groups to have used medication for their asthma, they were more likely to have seen a doctor. In 1995, 7% of 0-14 year olds with asthma had seen a doctor about it in the previous two weeks. Among adults, the proportion who consulted a doctor increased steadily with age, from 2% of 15-24 year olds to 6% of those aged 65 years and over.

Even with careful management, acute attacks of asthma cannot always be prevented and severe attacks may require treatment in hospital. The 1995 NHS estimated that 1% of children with asthma (6,400) had visited hospital casualty, emergency or outpatients units for asthma treatment during the two weeks before interview.

Hospital statistics compiled by the Australian Institute of Health and Welfare4 show that asthma is the most common medical condition for which children are admitted to hospital. For the year 1996-97, hospitals in Australia recorded asthma as the primary reason for 62,000 inpatient episodes, half of which related to children under 15 years of age. Asthma was the primary reason for 10% of all hospital inpatient episodes among 1-4 year olds and 5% among 5-14 year olds.

PEOPLE WHO TOOK RECENT(a) HEALTH-RELATED ACTIONS BECAUSE OF THEIR ASTHMA, 1995

Age group (years)

0-14
15-24
25-44
45-64
65 and over
Total
Type of action taken
%
%
%
%
%
%

Used medication
48.6
52.7
57.1
61.6
68.2
55.3
Consulted doctor
6.9
2.2
3.5
4.4
5.6
4.6
Took day(s) off work/school
3.8
1.2
0.8
0.5*
* *
1.7
Other day(s) of reduced activity
2.5
0.7
1.3
1.5
2.5
1.7
Consulted other health professional
1.5
1.1
0.5
0.6*
* *
1.0
Hospital casualty/emergency/outpatients
1.0
0.7
* *
* *
* *
0.6
Total who took action for asthma(b)(c)
49.3
53.0
57.5
62.0
68.7
55.8
Total who had asthma
100.0
100.0
100.0
100.0
100.0
100.0

Total who had asthma ('000)
632.6
404.9
508.3
315.5
180.0
2,041.4

(a) During the two weeks before interview.
(b) People may have taken more than one type of action. Therefore components may not add to totals.
(c) Includes people who took vitamins/minerals, used natural/herbal medicines, visited a hospital day clinic or were admitted to hospital as inpatients.

Source: Unpublished data, 1995 National Health Survey.


Reduced activity due to asthma
The 1995 NHS estimated that 1 in 26 children with asthma had taken one or more days off school (in the past two weeks) because of their asthma. Other than days away from school, 1 in 40 children with asthma had reduced their usual activities (e.g. sport, exercise) or stayed in bed for one or more days during the previous two weeks because of their asthma.

On the whole, asthma appeared to cause less disruption to the usual activities of adults than of children. For example, fewer than 1% of 25-64 year olds with asthma had taken a day off work in the past two weeks because of their asthma. With the exception of older people (aged 65 years and over), adults were also less likely than children to have had other days of reduced activity (i.e. other than days away from work or school) because of their asthma.


DEATHS DUE TO ASTHMA: AGE-STANDARDISED RATES(a)
(a) Age standardised death rate per 100,000 of the total population at 30 June 1991.

Source: Unpublished data, Causes of Death collection.


Deaths due to asthma
The risk of dying from asthma is relatively low. In 1997, asthma was the underlying cause of 715 deaths which represented 5% of deaths from respiratory diseases and less than 1% of all deaths in Australia. Asthma was recorded as a contributing cause in a further 1,157 deaths. As for most other causes of death, the rate of asthma deaths increases with age. In 1997, age-specific death rates from asthma ranged from less than 1 death per 100,000 of the population aged under 35 years, to just over 22 deaths per 100,000 of the population aged 65 years and over.

Age-standardised death rates from asthma (as the underlying cause of death) increased during the 1980s, peaking in 1989, but have since declined to below the 1982 rates for both males and females. Several researchers5,6,7 have found evidence to suggest that some of the increase in asthma death rates during the 1980s may have been due to diagnostic transfer, resulting in overstatement of asthma deaths, particularly among older people. Diagnostic transfer refers to a tendency to diagnose one condition rather than another owing to similarities in symptoms and changing recognition of diseases.


Endnotes

1 Jenkins, C.R. and Woolcock, A.J. 1997, ‘Asthma in adults’, Medical Journal of Australia, vol. 167, pp. 160-165.

2 Sporik, R., Holgate, S., Platt-Mills, T., Cogswell, J. 1990, ‘Exposure to house dust mite allergen (Der p1) and the development of asthma in childhood. A prospective study’, New England Journal of Medicine, vol. 323, pp. 502-507

3 National Health and Medical Research Council 1997, The health effects of passive smoking, A scientific information paper, AGPS, Canberra.

4 Australian Institute of Health and Welfare 1998, Australian Hospital Statistics 1996-97, AIHW, Canberra.

5 Jenkins, M.A., Rubinfeld, A., Robertson, C.F., Bowes, G. 1992, ‘Accuracy of asthma death statistics in Australia’, Australian Journal of Public Health, vol. 16, no. 4, pp. 427-429.

6 Campbell, D.A., McLennan, G., Coates, J.R., Frith, P.A., Gluyas, P.A., Latimer, K.M., Martin, A.J., Roder, D.M., Ruffin, R.E., Yellowlees, P.M. 1992, ‘Accuracy of asthma statistics from death certificates in South Australia’, Medical Journal of Australia, vol. 156, pp. 860-863.

7 National Health and Medical Research Council 1988, Asthma in Australia; Strategies for reducing morbidity and mortality, Report of the NHMRC Working Party on Asthma Associated Deaths, Canberra.


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