Morbidity and Burden of Disease (VCE SSCE Health and Human Development): Revision Notes

Morbidity and Burden of Disease

Understanding morbidity

Not all health conditions result in death, which is why it's important to examine how non-fatal conditions affect young people's health and wellbeing. This is where morbidity data becomes valuable.

Morbidity refers to ill health in an individual and the levels of ill health within a population. This includes disease, injury and disability. The morbidity rate measures the rate of ill health in a population during a given period.

There are two main ways to measure morbidity:

1. The number or rate of people reporting a condition (shown as percentages, incidence rates, or prevalence rates)
2. Years lost due to disability (YLD), where one YLD equals one 'healthy' year of life lost due to living with disease, injury or disability

By using both methods, we can identify which conditions are most common and which have the biggest impact on health and wellbeing among Australian youth.

Incidence and prevalence of health conditions

What are incidence and prevalence?

Incidence refers to the number (or rate) of new cases of a disease or condition in a population during a given period, usually 12 months. Think of incidence as the new cases flowing into the population.

Prevalence refers to the total number or proportion of cases of a particular disease or condition present in a population at a given time. Prevalence represents all existing cases at one point in time.

Both can be expressed as total numbers or as rates (typically per 1,000 or per 100,000 population).

Why this matters

Incidence data helps identify which conditions are increasing or decreasing in diagnosis. This assists governments and health organisations in allocating resources and taking action to improve youth health status. Prevalence data reveals how many individuals are currently suffering from conditions, helping with resource allocation and future planning.

Common health conditions among Australian youth

The table below shows estimated incidence rates (new cases per 1,000 population) for selected conditions among Australian youth in 2019:

Condition	Males 10-14	Males 15-19	Females 10-14	Females 15-19
Asthma	6.9	3.4	6.9	4.9
Migraine	16.5	12.7	26.5	24.3
Anxiety and depression	24.1	53.7	41.3	96.9
Eating disorders	8.1	19.3	8.5	18.4
Back and neck pain	14.0	19.7	17.1	25.1
Dental caries	428.9	519.3	437.1	520.4

Key patterns from this data:

• Anxiety and depression show notably high incidence rates, particularly among females aged 15-19 (96.9 per 1,000)
• Dental caries has the highest incidence rates across all groups
• Most conditions show higher rates in the older age group (15-19 years)
• Females generally experience higher rates than males for most conditions

Understanding these health conditions

Condition	Description
Asthma	When exposed to triggers (such as cigarette smoke or air pollution), the airway lining becomes inflamed and swollen, extra mucus is produced, and airway muscles tighten (bronchoconstriction). This narrows the airways, making breathing difficult.
Migraine	A neurological condition characterised by severe, throbbing headaches usually on one side of the head. Attacks can last from four hours to three days and are linked to spasms in blood vessels leading to the brain. They may occur infrequently or several times per week.
Anxiety and depression	Anxiety involves extreme worry that interferes with daily life, including panic attacks, physical fear reactions and avoidance behaviours. Depression involves constant feelings of sadness and loss of interest in normal activities without an identifiable reason.
Eating disorders	Mental illnesses including anorexia nervosa (restricted eating, weight loss, fear of weight gain), bulimia nervosa (binge eating followed by compensatory behaviours like over-exercising or vomiting), and binge eating disorder (uncontrolled eating episodes followed by guilt and distress).
Back and neck pain	Common among youth, often caused by poor posture, inappropriate exercise techniques, and carrying heavy schoolbags.
Dental caries	Also known as cavities or tooth decay, dental caries occur when tooth enamel breaks down due to excess acid in the mouth.

Calculating total cases and rates

Understanding how to calculate incidence and prevalence rates is essential for interpreting health data. The formulas are:

$\text{Total new cases} = \frac{\text{Population}}{1000} \times \text{Rate per 1000}$

$\text{Prevalence rate} = \frac{\text{Total cases}}{\text{Population} \div 1000}$

Prevalence data for selected conditions

The total number of cases (prevalence) for selected conditions in 2019:

Condition	Males 10-14	Males 15-19	Females 10-14	Females 15-19
Asthma	93,167	70,808	83,497	78,041
Migraine	68,041	87,662	85,606	136,670
Anxiety and depression	11,726	28,311	18,506	47,235
Eating disorders	1,644	5,856	4,687	18,290
Back and neck pain	19,818	37,283	22,384	43,828
Dental caries	175,180	202,670	72,405	196,332

Prevalence rates per 1,000 population for the same conditions:

Condition	Males 10-14	Males 15-19	Females 10-14	Females 15-19
Asthma	116.6	91.9	110.3	107.1
Migraine	76.4	113.7	113.1	187.6
Anxiety and depression	14.7	36.7	24.5	64.8
Eating disorders	2.1	7.6	6.2	25.1
Back and neck pain	24.8	48.4	29.6	60.1
Dental caries	219.2	262.9	227.8	269.4

Years lost due to disability (YLD)

What is YLD?

Years lost due to disability (YLD) measures the impact of morbidity on a group or population. While YLL (years of life lost) measures healthy years lost due to premature death, YLD measures healthy years lost because of living with illness, disease or disability.

Disability weights: making fair comparisons

Different conditions affect people in different ways. For example, asthma's impact differs significantly from losing a leg in a car crash. To address this challenge, the World Health Organization (WHO) has assigned disability weights to common conditions.

These weights indicate:

• The severity of the condition
• How much it interferes with normal life

YLD patterns by age and gender

This graph shows that:

• Males experience slightly more YLD than females up to age 5-9
• Females experience greater YLD numbers and rates in both 10-14 and 15-19 age groups
• The increase in mental disorders among females in these age groups is largely responsible for this change
• Both total YLD and YLD rates increase progressively with age

Leading causes of YLD among youth

For 10- to 14-year-olds:

The breakdown shows:

• Mental and substance use disorders: 33.18% (largest contributor)
• Skin disorders: 14.29%
• Injuries: 12.12%
• Respiratory diseases: 9.19%
• Diseases of the nervous system: 8.82%
• Musculoskeletal conditions: 5.9%
• All other diseases: 16.5%

For 15- to 19-year-olds:

The breakdown shows:

• Mental and substance use disorders: 42.46% (even more dominant)
• Injuries: 10.64%
• Musculoskeletal conditions: 10.11%
• Skin disorders: 9.73%
• Diseases of the nervous system: 8.41%
• Respiratory diseases: 5.19%
• All other diseases: 13.46%

Key conditions contributing to YLD

Condition	Description
Mental and substance use disorders	Include depression, anxiety, eating disorders, and alcohol and drug use disorders. These are the largest contributor to YLD among youth, indicating they have the greatest non-fatal impact on health status. These conditions are both common and can be quite severe.
Skin disorders	The third leading contributor to YLD, including acne, eczema, psoriasis and other forms of dermatitis (conditions causing skin irritation, inflammation, itching, dryness or rashes). These conditions are often long-lasting and can be severe.
Musculoskeletal conditions	Affect bones, muscles and connective tissues. Common examples include juvenile arthritis (joint pain and swelling in those under 16), back problems (affecting bones, joints, tissues, muscles and nerves), and joint reconstruction surgery (such as shoulder and knee reconstruction).
Respiratory diseases	Asthma and bronchitis account for the majority of YLD from respiratory conditions. Although more youth experience asthma than mental disorders, asthma is considered less severe and therefore contributes fewer YLD.

Burden of disease

Understanding burden of disease and DALY

Burden of disease is a concept that combines mortality data with morbidity data, allowing conditions that contribute differently to death and illness to be compared fairly. For example, cancer causes significant death and illness, while chronic conditions like asthma cause substantial illness but less death. Previously, comparing these conditions was difficult, making funding decisions challenging. Burden of disease data helps overcome this problem.

Burden of disease is measured in disability adjusted life years (DALY), where 1 DALY equals one year of healthy life lost due to premature death and time lived with illness, disease or injury.

Using DALY, we can equally compare:

• Conditions that cause death
• Conditions that cause disability and illness
• Conditions that cause both

Examples of DALY in practice

• A person who lived a healthy life but dies suddenly 30 years earlier than expected life expectancy contributes 30 DALY
• A person still alive but who has spent their last 10 years at only 'half health' contributes 5 DALY

Although ill health generally has greater effects towards the end of life, YLD can be contributed at any stage of life.

Leading causes of burden among youth

The ten leading causes of burden of disease and injury for 10- to 19-year-olds in Australia (2019):

Condition	10-14 years DALY	% of total	15-19 years DALY	% of total
Mental and substance use disorders	26,831	29.0%	52,696	34.7%
Injuries	14,083	15.2%	33,482	22.1%
Skin disorders	11,708	12.6%	11,760	7.7%
Neurological conditions	7,969	8.6%	11,375	7.5%
Respiratory diseases (including asthma)	7,967	8.6%	6,747	4.4%
Musculoskeletal conditions	4,905	5.3%	12,335	8.1%
Infectious diseases	3,762	4.1%	3,689	2.4%
Cancer	2,952	3.2%	3,843	2.5%
Infant and congenital conditions	2,103	2.3%	1,944	1.3%
All other conditions	10,348	11.2%	13,929	9.2%

Key patterns:

• Mental and substance use disorders are the leading cause in both age groups
• The burden from mental health increases with age (29% to 34.7%)
• Injuries become more significant in the older age group (15.2% to 22.1%)
• Musculoskeletal conditions nearly double in burden for older youth

Additional condition definitions

Neurological disorders common among youth include migraine and headache disorders, as well as epilepsy (a condition characterised by seizures caused by disrupted electrical activity in the brain).

Infectious diseases include respiratory infections, meningococcal infections, food poisoning, and sexually transmissible infections such as chlamydia, syphilis and gonorrhoea.

Infant and congenital conditions first occur before or just after birth, including:

• Down syndrome (genetic condition with three chromosomes on the 21st pair, causing distinct facial features, reduced muscle mass and impaired intelligence)
• Muscular dystrophy (progressive and irreversible muscle weakness and wasting)
• Birth defects (missing or ill-formed body structures with genetic, infectious or environmental origins)

YLD versus YLL among youth

In 2019, Australian youth aged 10-19 experienced:

• 202,944 YLD
• 41,484 YLL
• Total: 253,975 DALY

This breakdown chart shows:

• Mental and substance use disorders contribute almost entirely YLD (pink bars), with minimal YLL (blue bars)
• Injuries show a more balanced contribution of both YLD and YLL
• Most conditions contribute primarily through disability rather than death
• The combined burden emphasises the importance of both preventing death and managing chronic conditions

Case study: ACL injuries among Australian youth

An epidemic of anterior cruciate ligament (ACL) injuries demonstrates the burden of musculoskeletal conditions among young Australians. Key findings include:

The problem:

• Australia has the world's highest rates of ACL reconstructions
• Injuries are occurring in increasingly younger athletes, some as young as 7 or 8
• Nearly 200,000 ACL reconstructions performed in 15 years to 2015
• 74% increase in reconstructions among those under 25
• Biggest increase in children aged 5-14: 8.8% annual growth for girls, 7.7% for boys

Repeat injuries:

• Among 128 young people who had two ACL surgeries, almost 30% had a third injury
• This high rate raises concerns for future knee health

Long-term effects:

• Future knee reconstructions
• Debilitating pain through osteoarthritis
• Need to switch to lower-risk sports

Prevention:

• Many ACL injuries are preventable with proper agility training
• Proposed national prevention program costing $2-3 million
• Teaching volunteer coaches effective warm-up techniques
• Estimated to be cost-effective given surgery costs $142 million annually

Study tip: using correct units of measurement

When analysing or explaining burden of disease data, always use correct units of measurement. In the chart showing DALY by cause, the numbers are shown in thousands (represented by '000s). Therefore:

• Mental and substance use disorders contribute approximately 80,000 DALY (not 80 DALY)
• Injuries contribute approximately 48,000 DALY
• Always check the scale and units on graphs and tables