Comorbidities and Risk Factors

Worldwide incidence of asthma readmission is up to 40% (ref 1, intro).

NSW (ref 1,3)

A retrospective longitudinal study looking at 48,217 asthma hospitalisations in children aged 2-17 years reported that over 1 in 5 children hospitalised for asthma in NSW between 2007 and 2022 were readmitted for asthma within a year, costing an average AU$2593 per readmission. (ref 1)

The study included all children born in NSW between 2005 and 2015 who had at least one asthma hospitalisation across NSW between 2007 and 2022.

Findings (ref 1):

• 21.6% of children were readmitted to hospital due to asthma within 12 months
• readmitted children were younger than non-readmitted ones (mean age 3.8 vs 4.37) with 81% of readmitted children being aged 2-4 years (vs 65% of non-readmitted)
• overall incidence rate for the first asthma readmission within the 12 months was 23.8 per 100 person-years (95% CI 22.6 to 25.1)
• the incidence rate of asthma readmission was twice as high in children 2-4 years and went down with age up to the age group (28.7 per 100 person-years for 2-4 yo; 14.7 for 5-9 yo; 11.2 for 10-14 yo) but then increased again in older adolescents (18.0 per 100 person-years in 15-17 yo)
• the readmission incidence rate was highest in the first month following hospitalisation

• readmission incidence rate was higher in the more disadvantaged areas and major cities, implying socioeconomic disparities with higher population density, traffic congestion, and environmental pollution

• First readmission cost on average AU$2593 in direct medical cost per episode,  but increased with age up to 10-14yo: lowest cost in children 2-4 yo (AU$2867 per episode) and highest cost in children 10-14 yo (AU$4392 per episode).
• the medical cost of first asthma readmissions within 12 months was AU$ 15.6million.

Possible reasons:

• Hospital discharge without proper disease management, guideline-discordant asthma care, lack of education including reviewing inhaler technique and adequate counselling during discharge have been demonstrated to influence the risk of asthma readmission within the first few months of index hospitalisation
• Causal factors for higher readmission rate in younger children may include the high incidence of respiratory infections, particularly viral infections, environmental triggers such as environmental tobacco smoke, secondary smoking at home, traffic-related air pollution, moulds at home, dust-mite allergens, food allergens and inhalant allergens are causal risk factors for asthma readmissions among young children.

The same study/data was used to identify risk factors for these asthma readmissions (ref 3).

This second publication reported: (ref 3)

• 22% were readmitted within a year: 18% of these readmitted within 30 days (early readmission) and 82% readmitted after 30 days (late readmission)
• Most readmitted children were aged between 2 and 4 (77% of early readmissions, 81.5% of late readmissions)

Risk factors for early readmissions:(ref 3)

• children’s age 2–4 years (adjusted Relative Risk (adjusted risk ratio 1.71)
• No older siblings (1.26)
• Length of stay ≥ 2 days (1.42)
• Intensive care unit admission (2.27)
• Underlying chronic comorbidities and/or congenital anomalies (1.27)
• Admissions related to allergies or eczema (1.54)

Risk factors for late readmissions:(ref 3)

• Children’s age 2–4 years (1.93) – nearly twice as likely!
• No older siblings (1.09)
• Residence in the most socio‐economically disadvantaged areas (1.16)
• Residence in major cities (1.20)
• Index admission during spring (1.16) or summer (1.10)
• Length of stay ≥ 2 days (1.21)
• Admissions related to allergies or eczema (1.40)

VIC (ref 2)

A smaller study was conducted in VIC across 3 hospitals for 767 children 3-18 years hospitalised for asthma between 2017 and 2018. The study found that 34.3% of children were radmitted within 12 months, 69% of them being aged 3-5 yo.(ref 2)

note: the NSW data is stronger evidence as it is a population-based large study in NSW and included longer follow-up.

According to the Global Burden of Disease study 2021, a systematic review and meta-analysis including data from 389 sources for asthma reported that in 2021 there was:

• an estimated 260 million people with asthma worldwide
• forecast to reach 275 million people having asthma in 2050
• age standardised prevalence: 3340 per 100,000 in 2021, a 40% decrease compared to 1990 (5568 per 100,000), and expected to remain stable between 2021 and 2050.

Modifiable risk factors were responsible for 30% of the global asthma DALY burden, particularly high BMI in high-socio-demograhic (SDI) index settings, and occupational asthmagens in low SDI settings.

According to self-reported data from the NHS 2022, amongst people with asthma aged 18 and over:
– 19% reported that asthma interfered with daily activities 2 or more times in the past 4 weeks (vs 23% in 2017-18), including going to school or work, playing with friends, exercising, getting around places etc.
– 8.8% experienced very high level of psychological distress in the past 4 weeks compared to 11% in 2017-18
– 9.4% considered themselves to be in poor health compared to 7.6% in 2017-18.

Risk factors – Asthma Burden of Disease (AIHW 2024)
Risk factors attributable burden of asthma: the Burden of Disease study estimated that in 2024:
– 36% of asthma total burden was due/attributed to all risk factors combined
– 24% was due/attributed to being overweight (including obesity)
– 7% was due/attributed to tobacco use
– 5% was due/attributed to occupational exposures and hazards
Air pollution, although not directly linked to asthma burden, was linked to other respiratory conditions and was estimated to contribute 7.5% to the burden of Chronic Obstructive Pulmonary Disease.

Information from the burden of Disease study 2024:(ref 1)

In 2024, Asthma was the 10th leading contributor to the total burden of disease in Australia with a disability-adjusted life years (DALY) rate of 5.35 per 1,000 population (143,782 DALY, crude number), similar to 2023
– After adjustment for age structure, asthma was the 8th leading cause of total burden, with an age-standardised DALY rate of 5.3 DALY per 1,000, similar to 2023 (8th) but up from 9th in 2018 and 2015, and 10th in 2011 and 2003, with an increase by 8.5% in the last 21 years (from 4.9 per 1,000 in 2003; 4.4 in 2011; 5.0 in 2015; 5.2 in 2018; 5.3 in 2023 and 5.3 in 2024)
– 5.7% of the total asthma burden was fatal, 94.3% was non-fatal

By gender:
– Asthma ranked 6th in females of all ages for total burden (after adjusting for age) with an age-standardised DALY rate of 5.7 DALY per 1,000, up from 7th in 2018 and a 4.3% increase since 2003, but unchanged compared to 2023
– Asthma ranked 10th in males of all ages for total burden (after adjusting for age) with an age-standardised DALY rate of 4.9 DALY per 1,000, down from 9th in 2018 and a 13.5% increase since 2003, but unchanged compared to 2023

By age groups (age-specific DALY per 1,000), asthma ranked as leading cause of total burden of disease:
– Under 5 year-olds (0-4): 5th in females ( accounting for 2.9% of total burden) and in males (3.4% of total burden)
– under 1 year-olds: ranking 25th overall (24th in males, not in top 25 for females)
– 1-4 year-olds: ranking 1st in boys, girls and overall
– 5-9 year-olds: 1st in females, 2nd in males after Autism spectrum disorder, ranking 1st overall
– 10-14 year-olds: 2nd in females, 2nd in males and 2nd overall
– 5-14 year olds: 1st in females (accounting for 10.7% of burden) and 2nd in males (accounting for 12.8% of burden)
– 15-19 year-olds: 6th in females, 5th in males, 4th overall
– 20-24 year-olds: 5th in females, 8th in males, 6th overall
– 25-44 year olds: 4th in females (accounting for 4.7% of burden), not in the top 5 for males
For asthma burden for other age groups, see Fig 3.4 (Rank by number) on AIHW web report.

Note: to compare epidemiological data, it is usually preferred to use age-standardised statistics to ensure the differences are not caused by variations in age structure and an ageing population, unless the data is for specific age ranges in which case “crude” age-specific statistics are used.

Figure 3.5: Disease- or injury-specific summary of disease burden in Australia: Asthma

Risk factors attributable burden of asthma: it was estimated that in 2024
– 36% of asthma total burden was due/attributed to all risk factors combined
– 24% was due/attributed to being overweight (including obesity)
– 7% was due/attributed to tobacco use
– 5% was due/attributed to occupational exposures and hazards
Air pollution, although not directly linked to asthma burden, was linked to other respiratory conditions and was estimated to contribute 7.5% to the burden of Chronic Obstructive Pulmonary Disease.

Additional information reported in AIHW Asthma webpage: (ref 2)

In 2024, asthma accounted for:

• 2.5% of total disease burden (DALY), 4.3% of non-fatal burden (YLD) and 0.3% of fatal burden (YLL)
• within the respiratory disease group, it accounted for 35% of total disease burden, 51% of non-fatal burden and 5.3% of fatal burden

The rate of burden from asthma was higher in females vs males (1.2 times higher with 5.8 vs 4.9 DALY per 100,000 population)

Trends over time:

The age-adjusted rate of burden due to asthma increased between 2003 and 2024 from 4.9 to 5.3 DALY per 100,000. The increase was driven by non-fatal burden.

Age-standardised DALY rates due to asthma, 2003 to 2024:

The National Aboriginal and Torres Strait Islander Health Survey for the financial year 2022-2023  reported:
• 16.6% has asthma, up from 15.7% in 2018-2019 (note that the difference between 2018-2019 and 2022-2023 was not statistically significant)
• Asthma was the second most prevalent selected chronic condition after mental and behavioural conditions
• By remoteness: 18.2% of people living in non-remote areas had asthma, compared to 8.1% of people living in remote areas (the difference was statistically significant)
• Around two in four people (49%) had one or more selected chronic conditions in 2022–2023, up from 46% in 2018–2019.
• 29% of people aged 15 years and over smoked daily (excluding e-cigarettes or vaping devices), down from 37% in 2018–2019.

Prevalence data based on the National Health Survey 2022 indicated that:
– about 1.8 million (65%) of people living with asthma also had one or more chronic condition
– the top three comorbidities were: mental and behavioural conditions (41%), back problems (25%) and arthritis (23%)

A Cross-sectional survey of 6048 adult Australians with current asthma in the community (conducted in Feb-March 2021 during Covid measures) found that:
– 21.7% had difficult-to-treat asthma (DTTA)
– 85.4% of the participants with DTTA had at least 1 other chronic condition (comorbidity)

Note: DTTA was defined as severe asthma and/or poor asthma control and/or urgent asthma healthcare in previous 12 months despite medium-high dose ICS/LABA.

In 2022, 17.6% of people with a mental illness had asthma; 9.0% of people without a mental illness had asthma; and 11.5% of all people had asthma in Australia. Therefore, people with a mental illness where nearly twice as likely to have asthma than those without a mental illness. (proportions by states/territories and data for previous years are also available in Table 13A.58)

According to the NHS 2022, amongst adults (18+) with asthma in 2022:
– 1 in 7 (14.1%) were smoking daily
– 1 in 3 (32.2%) were ex-smokers
– 51.7% had never smoked (compared to 66.5% of people without any selected chronic condition)

Prevalence data based on the National Health Survey 2020-2021 indicated that: (ref1)
– Asthma is the fourth most commonly reported chronic condition at 10.7% of the population (9.4% in males and 12% in females), after mental or behavioural conditions (20%); back problems (16%) and arthritis (12%) (amongst the 9 selected chronic conditions reported in the survey)
– 20% of Australians had 2 or more chronic conditions in 2017-18 (23% of females vs 18% of males), becoming 51% of people aged 65+

According to the National health Survey 2020-2021, 78% of people aged 45 and over who currently have asthma also reported having one of the 9 selected chronic conditions. Specifically, in 2020-2021, among people aged 45 and over that have asthma: (ref 2)
– 42% had arthritis (compared with 26% among people without asthma)
– 33% had back problems (compared with 23% among people without asthma)
– 31% had heart, stroke, and vascular disease (compared with 22% among people without asthma)
– 20% had mental and behavioural conditions (compared with 11% among people without asthma)
– 14% had COPD (compared with 1.9% among people without asthma)
– 13% had osteoporosis or osteopenia (compared with 7.6% among people without asthma)

AIHW report providing summary of epidemiological data in First Nations peoples with asthma (prevalence, risk factors, quality of life, burden of disease, mortality, hospitalisations, ED). This report provides a nice summary and a single reference.

Prevalence (2018-2019 National Aboriginal and Torres Strait Islander Health survey (NATSIHS):
– Around 128,000 First Nations people reported having asthma (16%), down from 18% in 2012-13, making asthma the third most prevalent long-term condition reported in 2018-19.
– higher in females (18%) compared to males (13%)
– increased with age, from 12% in children aged 0–14 to 26% in those aged 55 and over
– 1.6 times as high for boys compared with girls (aged 0–14) (14% and 8.6%, respectively)
– 2.1 times as high for females compared with males aged 55 and over (34% and 16%, respectively)
– 1.6 times higher in First Nations people compared to non-Indigenous Australians after adjusting for age structure (18% and 11% age-standardised prevalence respectively)
– Prevalence decreased with increasing remoteness: 19% in Major Cities, 12% in Remote areas and 7% in Very remote areas
– Prevalence by states: 25% in ACT, 23% in SA, 22% in TAS, 19% in NSW, 18% in VIC, 14% in QLD, 13% in WA, 6% in NT

Hospitalisation rates (2021-2022):
– 1,800 hospitalisations with asthma as principal diagnosis in 2021-22 (Covid pandemic year), an hospitalisation rate of 200 per 100,000; a decrease by 30% compared to 2018-19 (non Covid-pandemic year; 290 per 100,000)
– highest for females aged 45–54 (469 per 100,000) and higher for females overall compared to males (250 vs 155 per 100,000)
– 1.8 times higher for boys compared to girls aged 0-14 (318 vs 173 per 100,000)
– 2.1 times higher in First Nations people compared to non-Indigenous Australians after adjusting for age structure (205 vs 100 per 100,000, age-adjusted)

Emergency Departments visits (2021-2022 Non-admitted Patient Emergency Department Care database):
– 5,400 ED presentations for asthma in 2021-22 (605 per 100,000 population, decreased by 14% compared to 700 per 100,000 in 2018-19)
– Highest for females 35-44 (1,063 per 100,000) then females 45-54 (1,014 per 100,000) then boys 0-14 (883 per 100,000)
– 1.6 times higher in boys vs gilrs aged 0-14 (883 vs 558 per 100,000)
– 1.4 times higher in females vs males overall (about 710 vs 500 per 100,000)
– 2.6 times higher in First Nations people compared to non-Indigenous Australians after adjusting for age structure (about 600 vs 230 per 100,000; age-standardised)

Mortality (2017-2021):
– 65 deaths over the 5 years, corresponding to a mortality rate of 1.7 deaths per 100,000 population (decreasing from 2.1 per 100,000 in 2015-2019)
– Mortality rate increases with age and is 1.6 times higher in females
– Mortality rates adjusted for age structure are 1.9 times higher in First Nations people compared to non-Indigenous Australians

Burden of Disease (Australian Burden of Disease Study 2018):
– 7th leading cause of disease burden in First Nations people, contributing 3.4% to the total burden
– Burden of asthma is greater in females (4.3%) compared to males (2.5%)
– 4th leading cause of non-fatal disease burden (5.7% of total non-fatal burden)

Risk factors for First Nations people with asthma compared to those without asthma (2018–2019 NATSIHS):
– Similar likelihood to be a current daily smoker (43% vs 40%)
– More likely to be insufficiently active (93% vs 87%)
– 1.3 times more likely to live with obesity (55% vs 43%)

Quality of life (2018–2019 NATSIHS) for adult First nations people with asthma compared to those without asthma:
– 2.5 times more likely to have poor health (18% vs 7.2%)
– 1.5 times more likely to experience high or very high levels of psychological distress (42% vs 28%)
– 62% had at least one other chronic condition – the top 3 comorbidities were arthritis (51%), mental and behavioural conditions (46%), and back problems (37%)

Asthma Management in First Nations people with asthma (2018–2019 NATSIHS):
– 56% reported using asthma medication within the last 2 weeks
– 32% had a written asthma action plan (32% of those in non-remote areas vs 27% of those in remote areas)

A Meta-analysis of observational studies totaling more than 5 millions subject reported strong or very strong associations of the following comorbidities in people with asthma, compared to people without asthma:
– Allergic rhinitis (OR 4.24, 95% CI 3.82–4.71)
– allergic conjunctivitis (OR 2.63, 95% CI 2.22–3.11)
– bronchiectasis (OR 4.89, 95% CI 4.48–5.34)
– hypertensive cardiomyopathy (OR 4.24, 95% CI 2.06–8.90)
– nasal congestion (OR 3.30, 95% CI 2.96–3.67)
– COPD (OR 6.23, 95% CI 4.43–8.77)
– chronic respiratory diseases (OR 12.85, 95% CI 10.14–16.29)

The associations were stronger for severe asthma patients, and also included comorbidities like:
– panic attacks (OR 3.16)
– phobia (OR 3.56)
– bipolar disorders (OR 6.16)
– hypertension (OR 3.35)

Note: Odds Ratios (OR) represent the relative risk of having the comorbidity, i.e OR=4.24 means that people with asthma are 4.24 times more likely to have allergic rhinitis than people without asthma.

2021 Report:

Some insights on tobacco (and e-cigarette) use and impact are available, including: (ref1)
– Tobacco is the leading cause of preventable burden in Australia: 8.6% of the total burden of disease and injury in 2018
– Tobacco contributed in 2018 to the burden of 39% of respiratory diseases
– Tobacco use is the leading cause of cancer in Australia (44% of cancer burden)
– In 2019, people living in remote and very remote areas were more likely to smoke daily (19.6%) than people living in Inner regional areas (13.4%) and Major cities (9.7%)
– E-cigarette use: in 2019, around 2 in 5 (39%) current smokers had used e-cigarettes in the lifetime, compared to 31% in 2016
There are several Tobacco infographic factsheets available

2025 report (ref 2) is available: https://www.aihw.gov.au/reports/alcohol/alcohol-tobacco-other-drugs-australia/contents/drug-types/tobacco

– Tobacco is the second leading cause of preventable burden in Australia: 7.6% of the total burden of disease and injury in 2024
– Tobacco contributed in 2024 to 71% of the burden of COPD
– Tobacco contributed to 73% of the burden of lung cancer

Asthma is significantly associated with an increased risk of lung cancer, with a hazard ratio of 1.34 (34% greater risk).
Note: this was a prospective cohort study based on UK biobank data in ABOUT 478 000 patients aged 37-73 years, recruited between 2006 and 2010 and followed up until 2019.

Article in the Australian Journal of General Practice summarising the increased risk of asthma associated with gas cooking, how to recognise the clinical implications in children and adults with asthma, and how to advocate for them.
Some reported facts: (please refer to article for exact references)
– 65% of houses in Australia use gas for cooking or heating
– The most important gas-related health effects are due to nitrogen dioxide (NO2) and carbon monoxide (CO)
– an estimated 30% of the risk of asthma for a child with current asthma living in a home with a gas stove comes from the stove
– across the community in Australia, 12% of childhood asthma is attributable to the use of gas stoves
– the risk of persistent asthma was also increased in Tasmanian aged 43-53 years living with gas heating and cooking, with OR 2.64 (1.22–5.70)
– questions about indoor gas exposure should be part of asthma review, and strategies discussed to reduce exposure

Overweight and obesity is responsible for approximately 24% of the burden of disease due to asthma in 2015.

Shows prevalence of asthma and other chronic conditions, as well as co-occurring conditions and patterns, in 2017-2018.

According to the 2017-2018 National Health Survey, among people with asthma (all ages);
– 24.8% also have arthritis
– 25% also have back problems
– 9.6% also have COPD
– 6.4% also have diabetes
– 7.2% also have heart, stroke or vascular disease
– 31.2% also have a mental or behavioural condition
– 6.9% also have osteoporosis

13.3% of people with asthma over the age of 45 have diabetes, compared to 10.5% of people without asthma
16.8% of people with asthma over the age of 45 have COPD, compared to 3.1% of people without asthma

People who are overweight or obese are more likely to have asthma, than people who are a normal weight.

74.2% of people with asthma over the age of 18 are overweight or obese, compared to 66% of people without asthma
42.3% of people with asthma over the age of 18 are obese, compared to 29.9% of people without asthma