Chronic respiratory conditions

What is asthma?

Asthma is a common chronic condition that affects the airways (the breathing passage that carries air into our lungs). People with asthma experience episodes of wheezing, shortness of breath, coughing, chest tightness and fatigue due to widespread narrowing of the airways (National Asthma Council Australia 2019a).

The symptoms of asthma are usually reversible, either with or without treatment. The severity of asthma ranges from mild, intermittent symptoms, causing few problems for the individual, to severe and persistent wheezing and shortness of breath. In a few people with asthma, the disease has a severe adverse impact on quality of life and may be life-threatening.

It is worth noting that it can be difficult to distinguish asthma from chronic obstructive pulmonary disease (COPD) because the symptoms of both conditions can be similar – both have obstruction to the airways, both are chronic inflammatory diseases that involve the small airways (Buist 2003). Although the current definitions of asthma and COPD overlap, there are some important features that distinguish typical COPD from typical asthma. For more information, see Chronic obstructive pulmonary disease (COPD).

In addition, clinical symptoms of asthma and bronchiectasis may overlap significantly as symptoms of cough, sputum and dyspnoea can occur in either asthma or bronchiectasis (Kang et al. 2014). Although these two diseases present several common characteristics, they have different clinical outcomes. Therefore, it is important to differentiate them at early stages of diagnosis, so appropriate therapeutic measures can be adopted (Athanazio 2012). For more information, see Bronchiectasis.

What causes asthma?

The fundamental causes of asthma are not completely understood. The strongest risk factors for developing asthma are a combination of genetic predisposition with environmental exposure to inhaled substances and particles that may provoke allergic reactions or irritate the airways, such as:

• viral respiratory infections
• indoor allergens (for example, house dust mites in bedding, carpets and stuffed furniture, pollution and pet dander)
• outdoor allergens (such as pollens and moulds)
• tobacco smoke
• chemical irritants in the workplace
• air pollution
• strong odours, such as perfume.

Other triggers can include cold air, change in temperature, thunderstorms, extreme emotional arousal such as anger or fear, hormonal changes, pregnancy and physical exercise. Certain medications can also trigger asthma: aspirin and other non-steroid anti-inflammatory drugs, and beta-blockers (used to treat high blood pressure, heart conditions and migraine) (WHO 2017).

How common is asthma?

Around 2.7 million Australians (11% of the total population) have asthma, based on self‑reported data from the 2017–18 Australian Bureau of Statistics (ABS) National Health Survey (NHS) (ABS 2018).

Prevalence by age and sex

Based on the 2017–18 NHS, among those aged 0–14 asthma was more common among boys. Conversely, among those aged 25–34 and 45 and over asthma was more common among women. Prevalence was similar among males and females aged 15–24 and 35–44 (Figure 1). This change in prevalence for men and women in adulthood is likely due to a complex interaction between changing airway size and hormonal changes that occur during adolescent development, as well as differences in environmental exposures (Almqvist et al. 2007).

Figure 1: Prevalence of asthma, by sex and age group, 2017–18

Note: Asthma refers to people who self-reported that they were diagnosed by a doctor or nurse as having asthma (current and long-term).

Source: ABS 2019a (Data table).

Prevalence in Aboriginal and Torres Strait Islander people

In 2018–19, 16% of Aboriginal and Torres Strait Islander people had asthma (an estimated 128,000 people), with a higher rate among females (18%) compared with males (13%) (ABS 2019b). The prevalence of asthma among Indigenous Australian was 1.6 times as high as non-Indigenous Australians, after adjusting for difference in age structure. The difference in asthma prevalence between Indigenous and non-Indigenous Australians exists across all age groups, but is more marked for older adults (Figure 2).

Figure 2: Prevalence of asthma, by age and Indigenous status, 2018–19

Note: Asthma refers to people who self-reported that they were diagnosed by a doctor or nurse as having asthma (current and long-term).

Sources: ABS 2019a; ABS 2019b (Data table).

Inequalities

The rate of asthma varies by remoteness and socioeconomic area.

For remoteness:

• the variation for males was not significant
• for females, the prevalence of asthma was highest for those living in Outer regional areas (15%) compared with those living in Major cities (11%).

For socioeconomic area:

• overall, the prevalence of asthma was highest for people living in the lowest socioeconomic area (13%) compared with those living in the highest socioeconomic area (10%)
• prevalence for males and females varies by socioeconomic area

Figure 3: Prevalence of asthma, by sex, remoteness and socioeconomic area, 2017–18

Notes

1. Rates have been age-standardised to the 2001 Australian Standard Population as at 30 June 2001. Age groups: 0–14, 15–24, 25–34, 35–44, 45–54, 55–64, 65–74, 75+.
2. Remoteness is classified according to the Australian Statistical Geography Standard (ASGS) 2016 Remoteness Areas structure based on area of residence.
3. Socioeconomic areas are classified according to using the Index of Relative Socio-Economic Disadvantage (IRSD) based on area of residence.

Source: ABS 2019a (Data table).

Impact of asthma

How does asthma affect quality of life?

Asthma has varying degrees of impact on the physical, psychological and social wellbeing of people living with the condition, depending on disease severity and the level of control.. People with asthma are more likely to describe themselves as having a poor quality of life. This is more pronounced among people with severe or poorly controlled asthma (Australian Centre for Asthma Monitoring 2004; Australian Centre for Asthma Monitoring 2011). Asthma is described as well-controlled when there are few symptoms and little reliever use (e.g. less than 2 days/week), and no night waking or limitation of activity. A survey conducted in 2012 of 2,686 Australians aged 16 years and over with current asthma found that asthma was not well-controlled in almost half (45%) of people. More than half of this group were not using a preventer inhaler, or were using it infrequently (Reddel et al. 2015).

In 2017–18, self-assessed health status among people with asthma aged 15 and over was, on average, worse than among those without asthma. For example, people with asthma were less likely to describe themselves as having excellent health compared with people without asthma (11% and 23%, respectively), and more likely to describe themselves as having fair health compared with people without asthma (16% and 9.9%, respectively). Conversely, people with asthma were more likely to describe themselves as having poor health compared with people without asthma (7.4% and 3.0%, respectively) (Figure 4).

Figure 4: Self-assessed health of people aged 15 and over with and without asthma, 2017–18

Note: Rates have been age-standardised to the 2001 Australian Standard Population as at 30 June 2001. Age groups: 15–24, 25–34, 35–44, 45–54, 55–64, 65–74, 75+.

Source: ABS 2019a (Data table).

In 2017─18, people with asthma were more likely to experience high (15%) and very high (11%) levels of psychological distress compared with those without asthma (8.7% and 3.4%, respectively) (Figure 5).

Figure 5: Psychological distress experienced by people aged 18 and over with and without asthma, 2017–18

Notes

1. Rates have been age-standardised to the 2001 Australian Standard Population as at 30 June 2001. Age groups: 18–24, 25–34, 35–44, 45–54, 55–64, 65–69, 70–74, 75–79, 80–84, 85+.
2. Psychological distress is measured using the Kessler Psychological Distress Scale (K10), which involves 10 questions about negative emotional states experienced in the previous 4 weeks. The scores are grouped into Low: K10 score 10–15, Moderate: 16–21, High: 22–29, Very high: 30–50.

Source: ABS 2019a (Data table).
 

In 2017–18, people with asthma were more likely to experience moderate (27%), severe (11%) and very severe (2.8%) bodily pain compared with people without asthma (17%, 5.4% and 1.3%, respectively) (Figure 6).

Figure 6: Pain experienced by people aged 18 and over with and without asthma, 2017–18

Notes

1. Rates have been age-standardised to the 2001 Australian Standard Population as at 30 June 2001. Age groups: 18–24, 25–34, 35–44, 45–54, 55–64, 65–69, 70–74, 75–79, 80–84, 85+.
2. Bodily pain experienced in the 4 weeks prior to interview.

Source: ABS 2019a (Data table).

In 2017─18, people aged 15 to 64 years with asthma were slightly less likely to be employed (73%) compared with people without asthma (77%) (Figure 7).

Figure 7: Workforce participation of people aged 15–64 with and without asthma, 2017–18

Note: Rates have been age-standardised to the 2001 Australian Standard Population as at 30 June 2001. Age groups: 15–24, 25–34, 35–44, 45–54, 55–64.

Source: ABS 2019a (Data table).

Deaths

Death from asthma is uncommon and effective management can reduce the risk even further. In 2018, there were 389 deaths due to asthma in Australia (0.2% of all deaths), which corresponds to a mortality rate of 1.3 per 100,000 population. The statistics presented in this section relate to deaths where asthma was listed as the underlying cause of death.

During the past decade, the overall trend of death due to asthma has decreased from 1.7 deaths per 100,000 population in 2009 and 2010, to 1.3 deaths per 100,000 population in 2018.

Attribution of death due to asthma is more certain among those aged 5–34, thus this age group is commonly used for examining time trends. There has been little change in the rate of mortality due to asthma in this age group over the last 10 years, with the rate ranging from 0.2 to 0.4 per 100,000 population.

For information on long-term trends, see General Record of Incidence of Mortality (GRIM) books. For more information on how deaths are registered, coded and updated, see Deaths data.

Figure 8: Age-standardised death rate due to asthma, by sex, 2009–2018

Higher death rate from asthma in certain population groups

Certain population groups have a higher mortality rate due to asthma. Asthma mortality rates increased with increasing remoteness of residence. Mortality rates due to asthma were higher among people residing in Outer regional (1.6 per 100,000 population) and Remote and very remote areas (1.9 per 100,000 population) than in Major cities and Inner Regional areas (1.2 and 1.4 per 100,000 population, respectively). Meanwhile, the mortality rate was higher among people residing in the lowest socioeconomic area (2.4 per 100,000 population) compared to those residing in the highest socioeconomic area (1.3 per 100,000 population) (AIHW: Poulos et al. 2014).

In addition, Aboriginal and Torres Strait Islander people experience higher asthma mortality rates than non-Indigenous Australians. In the 5-year period from 2014–2018, 63 Aboriginal and Torres Strait Islander people died from asthma, with a mortality rate of 1.8 per 100,000 population (based on five jurisdictions with adequate Indigenous identification (NSW, Qld, WA, SA and NT)). After adjusting for differences in age structure, the mortality rate of asthma among Indigenous Australians was 2.2 times as high as non-Indigenous Australians (3.4 compared with 1.5 per 100,000 population).

The mortality rate differences between these population subgroups may be due to differences in smoking rates, access to health services, or other social and environmental factors. Smoking rates are higher among people living in more remote areas, among people living in areas of lower socioeconomic status, and among Indigenous Australians (AIHW 2018).

Burden of disease

Burden of disease measures the gap between the ideal of living to old age in good health, and the current situation where healthy life is shortened or lost by illness, injury, disability and death (AIHW 2019a). It combines health loss from living with illness and injury (non-fatal burden, or years lived with disability, or YLD) and dying prematurely (fatal burden, or years of life lost, or YLL) to estimate total health loss (total burden, or disability-adjusted life years, or DALY). One DALY is one year of 'healthy life' lost due to illness and/or death.

Asthma affects people of all ages and has a substantial impact on the community. In Australia, asthma accounted for 34% of the total burden of disease due to respiratory conditions and 2.5% of the total disease burden in 2015 (AIHW 2019a). Between 2003 and 2015, there was a 3.1% increase in the total disease burden from asthma.

Asthma was the leading cause of total burden in children aged 5–14 years, contributing 14% of total burden for boys and 12% of total burden for girls in 2015 (AIHW 2019a).

However, most of the disease burden due to asthma consisted of non-fatal burden (93.7%) rather than fatal burden (6.3%) in 2015. Among children aged 0–14, asthma was the leading cause of non-fatal burden. Among people aged 15 and over, asthma still caused a substantial non-fatal burden but was ranked progressively lower with increasing age (AIHW 2019a).

In the younger age groups (ages 0–14), the rate of non-fatal burden (YLD) due to asthma was higher in males than females (Figure 9). The rate of fatal burden (YLL) was highest among those aged 75 and over for both males and females.

Figure 9: Burden of disease due to asthma, age-specific rate, by sex and age, 2015

Variation across population groups

The asthma disease burden varies across different population groups. The rate of total burden (DALY) due to asthma in Remote and very remote areas was 1.3 times as high as the rate in Major cities. Meanwhile, the rate of total burden (DALY) due to asthma in the lowest socioeconomic area was 1.8 times as high as the rate for the highest socioeconomic area. People living in Inner regional and Outer regional areas had a higher rate of fatal burden (YLL) than those living in Major cities and Remote and very remote areas (Figure 10).

Figure 10: Burden of disease due to asthma, age-standardised rate, by remoteness and socioeconomic area, 2015

Disease expenditure

In 2015–16, asthma cost the Australian health system an estimated $770 million, representing 19% of disease expenditure on respiratory conditions and 0.7% of total disease expenditure (AIHW 2019b).

This expenditure consisted of:

• $205 million for hospitals (27% of total expenditure on asthma)
• $163 million for non-hospital medical services (21%)
• $383 million for pharmaceuticals (50%)

Figure 11: Health expenditure on asthma, by area of expenditure and sex, 2015–16

Treatment and management of asthma

In general, symptoms of asthma are easily controlled in most people by making lifestyle changes and using medications, so they can have normal lives. The main aims of asthma treatments are:

• to stop asthma from interfering with school, work or play
• to prevent flare-ups or ‘attacks’
• to keep symptoms under control
• to keep lungs as healthy as possible (National Asthma Council Australia 2020).

What medicines are used to treat asthma?

There are several medicines available to treat asthma. Different asthma medicines are used to achieve different goals, as follows:

• Relievers are medicines used for the rapid relief of asthma symptoms when they occur. They can also be used before exercise, to prevent exercise-induced bronchoconstriction (constriction of the airways).
• Preventers are medicines used every day in asthma control to minimise symptoms and reduce the likelihood of episodes or flare-ups. Inhaled corticosteroids are the most commonly used preventers.
• Other medicines are used for management of difficult-to-treat asthma or as add-on options for management of severe asthma flare-ups.

Based on self-reported survey data, one-third (33%) of Australians with asthma had taken a respiratory medicine in the last 2 weeks in 2017–18 (ABS 2018). These medicines may have been used to treat asthma or another respiratory condition, as most of the medicines used for asthma are also used for patients with other chronic lung diseases, in particular chronic obstructive pulmonary disease (COPD).

For more detailed information about medicines used to treat asthma, refer to Australian Asthma Handbook, Version 2.0. It provides Australia’s national guidelines for asthma management.

Management of asthma

As asthma is a chronic disease, it has to be cared for all the time, not just when symptoms are present. The four parts of managing asthma are:

• Identify and minimise exposure to asthma triggers.
• Understand and use medications as prescribed so as to have good asthma control.
• Monitor asthma to recognise signs when it is getting worse.
• Know what to do when asthma gets worse (Stanford Children’s Health 2020).

For more detailed information about management of asthma for different population groups, refer to the Australian Asthma Handbook, Version 2.0: Management for children, adolescents, and adults.

What role do GPs play in managing asthma?

General practitioners (GPs) play a central role in the management of asthma in the community. This role includes assessment, diagnosis, prescription of regular medications, education, provision of written action plans, and regular review as well as managing asthma flare-ups. Asthma-related visits to GPs may occur for a variety of reasons, including:

• the acute or reactive management of asthma symptoms
• a review during or following a flare-up
• a review or initiation of a written action plan
• a visit for maintenance activities, such as monitoring and prescription of regular medications
• review asthma with other possible co-morbidities
• referral to a specialist and other health professionals.

In 2012, a survey of 2,686 Australians aged 16 and over with current asthma identified that 628 participants (23%) had visited a GP urgently about asthma at least once during the previous year, and 269 participants (10%) had attended a hospital or emergency department one or more times, with, in total, 769 participants (29%) reporting an urgent visit (urgent GP visit and/or hospital or emergency department visit) (Reddel et al. 2015).

According to the Bettering the Evaluation and Care of Health (BEACH) survey, asthma was one of the most frequently managed chronic problems in the decade up to 2015–16 (Britt et al. 2016). In the ten-year period from 2006–07 to 2015–16, the estimated rate of asthma management in general practice declined from 2.3 in 100 encounters to 2.0 in 100 encounters (Figure 12). It is worth noting that there is currently no nationally consistent primary health care data collection to monitor provision of care by GPs.

Figure 12: General practice encounters for asthma, all ages, 2006–07 to 2015–16

Notes
1. Asthma is classified according to International Classification of Primary Care, 2nd edition (ICPC-2) code R96.
2. The Bettering the Evaluation and Care of Health (BEACH) year is from April to March
3. An encounter relates to a consultation between a patient and a GP.
4. Statistics on general practice activities based on BEACH data are derived from a random sample survey of GPs and their encounters with patients, and should be interpreted with caution.

Source: Britt et al. 2016 (Data table).

An asthma action plan is a written self-management plan which is prepared for patients with asthma by a health care professional and can help people with asthma to manage their condition and reduce the severity of acute asthma flare-ups. There is no ‘standard’ asthma action plan, as everyone’s asthma is different. A patient’s plan needs to be developed to deal with his/her own triggers, signs and symptoms, and medication. Asthma action plans have formed part of the National Asthma Council Australia's guidelines for the management of asthma for 30 years (National Asthma Campaign 1990) and have been promoted in public education campaigns (including by the National Asthma Council Australia) on the basis that individualised written action plans improve asthma health outcomes (National Asthma Council Australia 2019a).

Despite the Australian Asthma Handbook recommending all people with asthma have an asthma action plan, many people with asthma do not have a current written plan. In 2017–18, an estimated 839,000 (31%) people with asthma across all ages had a written asthma action plan (ABS 2018). Over two-third of children aged 0–14 had an asthma action plan (67%), however, this rate in people aged 15 and over was only about one‑quarter (24%) (Figure 13). The results indicate that children aged 0–14 were the most likely to have a written asthma action plan compared with other age groups.

Figure 13: Proportion of people with asthma who have a written asthma action plan, by age group, 2017–18

Note: Asthma refers to people who self-reported that they were diagnosed by a doctor or nurse as having asthma (current and long-term).

Source: ABS 2019 (Data table).

The National Asthma Strategy

The National Asthma Strategy 2018 (the Strategy) was launched in January 2018. The Strategy aims to outline Australia’s national response to asthma and inform how existing limited health care resources can be better coordinated and targeted across all levels of government (Department of Health 2017). The Strategy identifies the most effective and appropriate interventions to reduce the impact of asthma in the community and continue to be an international leader in asthma prevention, management and research (Department of Health 2017). In 2019, the AIHW reported on the 10 national asthma indicators to monitor the outcome measures associated with the Strategy. For more information, see National Asthma Strategy 2018, and National asthma indicators – an interactive overview.

What role do hospitals play in treating asthma?

People with asthma require admission to hospital when flare ups or ‘attacks’ are potentially life-threatening or when they cannot be managed at home or by a GP. Data from the AIHW National Hospital Morbidity Database (NHMD) show that in 2020–21, there were 25,000 hospitalisations where asthma was the principal diagnosis. The age-standardised rate of hospitalisations for asthma was 100 per 100,000 population. The rate among children aged 0–14 (225 per 100,000 population) was markedly higher than the rate among people aged 15 and over (68 per 100,000 population) (Figure 14).

During the last decade, the rate of hospitalisations where asthma was the principal diagnosis for children aged 0–14 decreased overall, falling from 505 per 100,000 population in 2010–11 to 225 per 100,000 population in 2020–21. During this time, the proportion of children hospitalised overnight decreased from 79 to 64% with an average length of stay in hospital in 2020–21 of 1.5 days. Over the same period, the rate of hospitalisations for asthma for those aged 15 and over fluctuated between 92 per 100,000 in 2010–11 and 68 per 100,000 population in 2020–21, peaking at 115 separations per 100,000 in 2016–17. The proportion of overnight stays also decreased from 77 to 63% averaging 3.1 bed days in 2020–21 (Figure 15).

Hospitalisation rates differ by sex and age (Figure 14). In 2020–21, boys aged 0–14 were 1.6 times as likely as girls of the same age to be admitted to hospital for asthma. Conversely, of those aged 15 and over, females were 2.3 times as likely as males to be admitted to hospital for asthma. These differences in hospitalisation by sex and age reflect in part the difference in the prevalence of asthma – which is more common in boys than girls for those under 15, and generally more common in females than in males for those over 25.

Figure 14: Rate of hospitalisation for asthma, by sex and age, 2020–21

Age profile of hospitalisations for asthma compared with hospitalisations for all causes

While most hospitalisations for all causes in 2020–21 were for older people, 43% of the 25,000 hospitalisations for a primary diagnosis of asthma in Australia were for children aged 0–14 (Figure 15). The age profile of hospitalisations for asthma was much younger compared with hospitalisations for all causes in the same year.

Figure 15: Rate of hospitalisations for asthma (principal diagnosis) by sex, 2010–11 to 2020–21

Seasonal variation in hospitalisations for asthma

Among children, the peaks for asthma hospitalisations occur in late summer (February) and autumn (May) (Figure 16). The peak in February is likely related to respiratory infections associated with returns to school and childcare after the summer break. This has been found during similar peaks in September in Northern Hemisphere countries; lower use of preventer medication during holidays may also contribute.

Among adults, hospitalisations for asthma are highest in winter and early spring (June through to September), particularly in people aged 65 years and older (Figure 16). This coincides with the annual winter ‘flu’ season and may reflect the rise in respiratory infections observed then.

2020 was an exception to this general trend, and there was a large dip in hospitalisations in April and May for all agegroups. This is likely due to lockdown mandates related to COVID-19 across the nation.

Figure 16: Monthly variation in hospitalisations due to asthma, by age group, 2020

Comorbidities of asthma

Some people with asthma have other chronic and long-term conditions. This is called ‘comorbidity’, which describes any additional disease that is experienced by a person with a disease of interest (the index disease). For people with asthma, having a comorbid chronic condition can have important implications for their health outcomes, quality of life and treatment choices.

Australians diagnosed with one or more chronic conditions often have complex health needs, die prematurely and have poorer overall quality of life (AIHW 2018). In terms of comorbidities, in 2017─18 one in five Australians (20%) had two or more chronic conditions (ABS 2018). The chance of developing chronic conditions increases with age, and since asthma often starts early in life, people with asthma are likely to develop another chronic condition during their lifespan (AIHW 2019d).

The chronic conditions that have been selected for this asthma comorbidity analysis are: arthritis, back problems, cancer, chronic obstructive pulmonary disease (COPD), diabetes, heart, stroke and vascular disease, kidney disease, mental and behavioural conditions and osteoporosis. They have been selected because they are common in the general community, pose significant health problems and have been the focus of ongoing national surveillance efforts and action can be taken to prevent their occurrence (AIHW 2019d). Other chronic conditions that are commonly found in people with asthma, and that can impact on asthma, include obesity, allergic rhinitis, obstructive sleep apnoea, and gastro-oesophageal reflux disease (Boulet 2009; Caughey et al. 2008; Cazzola et al. 2012).

The National Asthma Strategy 2018 (the Strategy) was launched in January 2018. The Strategy ‘aims to outline Australia’s national response to asthma and inform how existing limited health care resources can be better coordinated and targeted across all levels of government’ (Department of Health 2017). The Strategy identifies the most effective and appropriate interventions to reduce the impact of asthma in the community and continue to be an international leader in asthma prevention, management and research (Department of Health 2017). The Strategy notes that ‘the presence of one or more comorbid conditions in people with asthma is likely to compromise their quality of life and may complicate their management of asthma’ (Department of Health 2017). The AIHW has monitored and reported on the outcome measures associated with The Strategy by reporting on the 10 national asthma indicators. For more information, see National asthma indicators – an interactive overview and National Asthma Strategy 2018.

Management of asthma includes medicines to minimise symptoms such as shortness of breath, wheezing and coughing, and to reduce the risk of adverse outcomes, such as flare-ups (AIHW 2019d).

Treatment of comorbidities depends on individual patient needs. As recommended in the Australian Asthma Handbook, some comorbidities such as obesity, mental illness, allergic rhinitis and obstructive sleep apnoea, should be treated not only to improve patient health outcomes, but to also reduce their impact on asthma control and risk of flare‑ups (National Asthma Council Australia 2019).

Medications prescribed for some comorbidities may interact with one another, which can cause problems for people with asthma. One example is beta-blockers, a treatment sometimes used for cardiovascular disease, glaucoma or anxiety. In people with asthma, beta-blockers given by tablet or eye-drops can cause severe asthma flare-ups, requiring more intense treatment and management (AIHW 2019d). Another example is non-steroidal anti-inflammatory medications (NSAIDs) including aspirin, which may be used to treat cardiovascular disease or arthritis. These medications can cause severe flare-ups in around 7% of people with asthma (Rajan et al. 2015).

For patients who have both asthma and COPD, treatment usually includes inhaled corticosteroids (anti-inflammatory medications) and long-acting bronchodilators together with management of modifiable risk factors (such as smoking cessation and increasing physical activity), pulmonary rehabilitation, and influenza vaccinations (National Asthma Council Australia 2019). Short-acting bronchodilators are also to be used as needed for symptom relief.

Due to the potential for interactions between different chronic conditions and the medications used to treat them, it is important that people with asthma tell their doctor(s) about any other conditions that they have, and any other treatment they are taking, so that their health can be carefully monitored.

Number of comorbid chronic conditions in people with asthma

An estimated 2.7 million Australians (11% of the total population) currently have asthma, based on self-reported data from the 2017–18 National Health Survey (ABS 2018a). Of these, around 1.6 million people (6.6% of the total population) also had one or more of the following selected chronic conditions:

• arthritis
• back problems
• cancer
• chronic obstructive pulmonary disease (COPD)
• diabetes
• heart, stroke and vascular disease
• kidney disease
• mental and behavioural conditions
• osteoporosis.

These 9 chronic conditions have been selected because they are common in the general community, pose significant health problems, have been the focus of ongoing national surveillance efforts, and action can be taken to prevent their occurrence.

Asthma affects people of all ages; however, many of the people with asthma and comorbid conditions are older Australians, reflecting the fact that chronic conditions are more widespread in older age groups.

Additional chronic conditions that are commonly found in people with asthma, and that can impact on asthma, include allergic rhinitis, obstructive sleep apnoea, mental illness, nasal polyps (soft, painless, non-cancerous growths) and gastro-oesophageal reflux disease (GORD) (AIHW 2019d).

For all persons who had asthma, 41% had only asthma with none of the other selected chronic conditions, while 59% had at least one of the nine other selected chronic conditions (ABS 2018a). Of those aged 45 and over who had asthma, 20% had asthma only, and 81% had at least one other of the selected 9 chronic conditions (Figure 17). Over 1 in 4 (27%) had one other selected chronic condition, and 54% had 2 or more other selected chronic conditions.

Figure 17: Comorbidity of selected chronic conditions in people aged 45 and over with asthma, 2017–18

Notes
1. The 9 selected chronic conditions were arthritis, back problems, cancer, COPD, diabetes, heart, stroke and vascular disease, kidney disease, mental and behavioural conditions, and osteoporosis.
2. Proportions may not add to 100% due to rounding.

Source: ABS 2019 (Data table).

Types of comorbid chronic conditions in people with asthma

Among people aged 45 and over with asthma:

• 49% had arthritis (compared with 32% among people without asthma)
• 37% had back problems (compared with 24% among people without asthma)
• 34% had mental and behavioural conditions (compared with 20% among people without asthma)
• 17% had COPD (compared with 3.1% among people without asthma)
• 15% had heart, stroke and vascular disease (compared with 11% among people without asthma)
• 15% had osteoporosis (compared with 8.4% among people without asthma) (Figure 2).

Figure 18: Prevalence of other chronic conditions in people aged 45 and over with and without asthma, 2017–18

Notes
1. Asthma here refers to people who self-reported that they were diagnosed by a doctor or nurse as having asthma (current and long-term).
2. Proportions may not add to 100% as a person may have more than one additional diagnosis.

Source: ABS 2019 (Data table).

Risk factors associated with asthma

Asthma shares a number of risk factors with other chronic conditions, such as:

• Non-modifiable risk factors

• genetic predisposition (Beasley et al. 2015)

• Modifiable risk factors

• tobacco use (smoking or exposure to cigarette smoke)
• exposure to environmental hazards (for example, exposure to air pollutants)
• overweight/obesity
• sedentary lifestyle (Beasley et al. 2015)

• Other risk factors

• allergic rhinitis (Beasley et al. 2015).

Risk factors may increase the chance of developing asthma in the first place (either in childhood or as an adult), or may increase the chance that a person with asthma will develop additional health problems. Risk factors also vary according to the person's age, and according to the type of asthma that they have (AIHW 2019e). Finding a factor that is associated with asthma, or poor health outcomes in asthma, does not necessarily mean that the risk factor caused these problems, or that they can be prevented.

In people with asthma, risk factors associated with an increased risk of flare-ups include (Global Initiative for Asthma 2019):

• having frequent symptoms (e.g. more than 2 days/week)
• not taking preventer treatment regularly (medicines used every day in asthma control to minimise symptoms and reduce the likelihood of episodes or flare-ups. Inhaled corticosteroids are the most commonly used preventers) (National Asthma Council Australia 2019)
• frequent reliever inhaler use (medicines used for the rapid relief of asthma symptoms when they occur) (National Asthma Council Australia 2019)
• comorbidities (e.g. mental illness, obesity, chronic rhino sinusitis)
• major socioeconomic problems
• exposure to smoking; allergens; air pollution.

Common risk factors

Based on the 2017–18 National Health Survey (NHS), people with asthma were more likely to be current daily smokers, insufficiently physically active and/or obese, compared with those without asthma (see Figure 19). Risk factor definitions are included in Box 1 (in the data notes section below). These risk factors are also common among other chronic conditions.

Figure 19: Prevalence of selected risk factors in people aged 18 and over with and without asthma, 2017–18

Note: Obese is based on body mass index (BMI) for persons whose height and weight was measured and imputed. In 2017–18, 33.8% of respondents aged 18 years and over did not have a measured BMI. For these respondents, imputation was used to obtain BMI. For more information, see Appendix 2: Physical measurements in the 2017–18 National Health Survey (ABS 2018a).

Source: ABS 2019a (Data table).

Selected risk factors

Smoker status

Compared with people without asthma, people with asthma were more likely to be current daily smokers (17% compared with 13% for people without asthma), and less likely to have never smoked (50% compared with 55% for people without asthma) (see Figure 20).

Tobacco use or exposure to environmental tobacco smoke are risk factors associated with the development of asthma. The interaction between exposure to tobacco smoke and development of asthma symptoms varies with age. Parental smoking during pregnancy or infancy is linked to asthma symptoms in children, and smoking by a parent or child/adolescent is linked to asthma symptoms in adolescence (Gilliland et al. 2006).

For people who already have asthma, smoking or exposure to environmental tobacco smoke can increase the risk of flare-ups and need for emergency care for asthma (Osborne et al. 2007). In people with asthma, smoking is also associated with a reduced effectiveness of inhaled corticosteroids (Lazarus et al. 2007; Tomlinson et al. 2005).

Figure 20: Smoker status of people aged 18 and over with and without asthma, 2017–18

Source: ABS 2019a (Data table).

Physical activity

Sufficient physical activity (for example, regular exercise) is an important factor associated with positive health outcomes. Insufficient physical activity is a risk factor for several chronic conditions. It is also associated with overweight and obesity, and poorer health outcomes more generally. See box 1 for definitions of physical activity.

Evidence suggests that sedentary behaviour (as measured by television viewing) is associated with asthma symptoms in children (Mitchell et al. 2012). The association between physical activity and asthma symptoms may be complicated by the fact that, in some people who already have asthma, physical activity may trigger asthma symptoms, particularly if their asthma is poorly controlled.

Physical activity is generally recommended for adults and children with asthma as a way to manage the disease and improve quality of life (National Asthma Council Australia 2019).

Based on the 2017–18 NHS, people with asthma were slightly less likely than people without asthma to engage in sufficient physical activity (42% compared with 46% for people without asthma) (Figure 21).

Figure 21: Physical activity in people aged 18 and over with and without asthma, 2017–18

Source: ABS 2019a (Data table).

Body mass

People with asthma were 1.4 times as likely to be obese (by measured body mass index or BMI—see data notes) as people without asthma (42% with asthma compared with 30% without asthma) (Figure 22).

Studies show there are associations between overweight and obesity, as measured by BMI, and asthma, especially in high income countries (Beasley et al. 2015). Additionally, people with asthma who are overweight or obese often experience complications in treatment. For people who are overweight or obese, weight loss has been shown to reduce treatment complications and improve symptoms (Adeniyi & Young 2012; Juel et al. 2012). There is evidence of an association between being obese and developing asthma; however, the causative mechanisms between body mass and asthma are not currently well understood (Ford 2005; Kim et al. 2014)

Figure 22: Body mass index (BMI) distribution in people aged 18 and over with and without asthma, 2017–18

Note: Based on body mass index (BMI) for persons whose height and weight was measured and imputed. In 2017–18, 33.8% of respondents aged 18 years and over did not have a measured BMI. For these respondents, imputation was used to obtain BMI. For more information, see Appendix 2: Physical measurements in the 2017–18 National Health Survey (ABS 2018a).

Source: ABS 2019a (Data table).

Age differences in risk factors in people with asthma

For people with asthma, the prevalence of risk factors varies by age.

The prevalence of smoking in people with asthma was higher in the earlier years of life. People aged 18–44 and 45–64 with asthma were more likely to be a current daily smoker (19% and 20%, respectively) compared with those aged 65 and over (7.6%) (Figure 5). Smoke free laws, tobacco price increases and greater exposure to mass media campaigns may contribute to lower smoking rates among older Australians (Wakefield et al. 2014). GPs play an important role in encouraging and supporting people to quit smoking, especially when they have health problems caused or exacerbated by smoking, which are more common with increasing age (Royal Australian College of General Practice 2014).

Among people with asthma, 50% of those aged 18–44 were insufficiently physically active, compared with 60% of those aged 45–64 and 76% of those aged 65 and over. Those aged 45-64 were less likely to be insufficiently physically active compared with those aged 65 and over. Among those with asthma aged 18–44, 35% were obese, compared with 48% of those aged 45–64 and 49% of those aged 65 and over (Figure 23).

Figure 23: Prevalence of selected risk factors in people aged 18 and over with asthma, by age group, 2017–18

Note: Obese is based on body mass index (BMI) for persons whose height and weight was measured and imputed. In 2017–18, 33.8% of respondents aged 18 years and over did not have a measured BMI. For these respondents, imputation was used to obtain BMI. For more information, see Appendix 2: Physical measurements in the 2017–18 National Health Survey (ABS 2018a).

Source: ABS 2019a (Data table).