What are the major drivers of prevalent disability burden in young Australians?

The transition from puberty to young adulthood brings rapid changes in health. Anxiety, depression and eating disorders become common during teenage years. In young adulthood, substance misuse peaks and psychotic disorders become prominent,1 as do injury and sexual health problems. Also, childhood-onset disorders such as asthma, attention deficit hyperactivity disorder (ADHD) and autism, as well as complications from perinatal and congenital disorders, persist through these years. This complex, changing profile of adolescent health is challenging in terms of developing comprehensive policy responses.

Patterns of prevalent disability (ie, disability caused by current cases of disease or injury) are important starting points for planning health services. They indicate the most important diseases and injuries that are likely to need health services, and show how diseases and injuries may change when young people transition from using child health services to adult health services.

We undertook secondary analysis of data from the Australian Burden of Disease and Injury Study2,3 to compare the causes of prevalent disability for 10–24-year-old Australians in 2003 by sex and age group.

The Australian Burden of Disease and Injury Study estimated the prevalent years lived with disability (PYLD) caused by 170 diseases and injuries for Australians in 2003.2,3 PYLD are the healthy years of life lost in the year of the study by people who have the disease or injury. They are distinct from incident years lived with disability, which are the future years of healthy life lost from new cases of disease or injury.

PYLD are equal to the prevalence of disease or injury multiplied by a “disability weight”.4,5 The prevalence estimates that we used to calculate PYLD were derived from national or state level Australian epidemiological data, where available (further detail on data sources and modelling has been described previously2).

For younger adolescents (10–14-year-olds), older adolescents (15–19-year-olds), and young adults (20–24-year-olds), we present the rates of PYLD per 1000 population attributable to 22 broad causes, and the 10 leading individual causes of PYLD.

Our analysis of 2003 data from the Australian Burden of Disease and Injury Study showed that rates of prevalent disability increase by almost 50% from younger adolescence to young adulthood. Mental disorders are the largest contributor to disability, with anxiety and depression being the leading single cause. Eating disorders make a significant contribution to mental disability in young women, which is noteworthy given they have received less attention in policy than other mental disorders such as schizophrenia, which cause less disability at the population health level at these ages.

ADHD and autism cause more disability in younger adolescents than in older adolescents and young adults, while all the other mental disorders cause more disability in older adolescents and young adults. The decline in disability caused by ADHD is a result of the modelling of prevalence estimates, which assumed rapid remission of ADHD symptoms in young adults. The relative contribution of autism to disability declines with age because of higher rates of other causes of disability.

Ongoing physical health problems from childhood (such as asthma) and the disabling consequences of low birth weight and birth trauma continue to play substantial roles in the health of adolescents, particularly younger adolescents. Many of these adolescent physical health problems are associated with substantial concurrent mental health and behavioural problems, which require an integrated approach to care.6 Furthermore, as with autism spectrum disorders, many physical health problems will persist into adulthood, and the quality of the transition to adult health care will influence the level of future associated disability.7,8

Our findings have some limitations. First, because of the small numbers of cases of disease in the age groups studied, differences in PYLD by age may reflect inaccuracies in modelling rather than real variations. Second, the age of some of the prevalence estimates must also be considered. For example, the mental disorder data9 used in the Australian Burden of Disease and Injury Study predates the year of the study (2003) by 6 years. Third, the disability weights applied to each disorder were, with a few exceptions (eg, adult-onset hearing loss, childhood conditions), uniform across age groups, which may not reflect potential differences in experience of disability at different ages.

Nevertheless, our findings highlight the changing pattern of disability caused by physical and mental disorders along the developmental trajectory from early adolescence to young adulthood. Successful policy and service responses to the drivers of disability among youth must be informed by the nature of the causes of disability (physical v mental) and age of onset. Childhood-onset physical disorders (eg, asthma) and mental disorders (eg, ADHD and autism) require models of care that facilitate ongoing self-management and successful transitions to adult health services. These models exist for asthma,10 but few exist for autism and ADHD.11

Common mental disorders with adolescent and young adult onset, such as anxiety and depression, are most likely to be detected in primary care. However, there are significant challenges in identifying and managing these conditions, so it is not clear which models of care best address them.12,13 Schizophrenia and eating disorders have a similar age of onset, but usually require specialist care. For anorexia nervosa, family-based treatment can be effective in the context of comprehensive specialist treatment.14 For schizophrenia, early intervention programs have the potential to reduce the associated disability,15,16 but more evaluation of medium-term outcomes and generalisability is needed.17,18

The major contributors to disability in young Australians are a mixture of mental disorders (especially anxiety and depression, ADHD, autism, eating disorders and schizophrenia) and some physical disorders (including asthma, migraine, and the consequences of low birth weight and birth trauma). Changes in the patterns of prevalent disability from early adolescence to young adulthood are necessary for prioritising health service investment — although these alone are not sufficient.19-21 Policymakers also need to know how much burden can be averted by effective interventions (if these exist), and which interventions are the most cost-effective. Even so, the changing profile of disability burden between early adolescence and young adulthood should focus attention on the delivery of accessible and youth-friendly health care, as well as the effectiveness of transitions in care from child health services to adult health services.

1 Contribution of broad causes to total prevalent disability in young Australians in 2003, by age group

PYLD = prevalent years lived with disability. * Other causes are those that explain less than 5% of total PYLD in 10–24-year-olds — infectious and parasitic diseases, acute respiratory infections, maternal conditions, genitourinary diseases, skin diseases, nutritional deficiencies, cancers, other neoplasms, endocrine and metabolic disorders, cardiovascular disease, diabetes mellitus, diseases of the digestive system, musculoskeletal diseases, oral conditions and ill-defined conditions. † Injuries include intentional and non-intentional injuries.