d) Incidence and prevalence   

Incidence - refers to the number of new cases in a period of time, e.g. a year.          Q

Prevalence - refers to the total number of cases present in the community at a particular point in time.

There is considerable uncertainty about the incidence and prevalence of ABI in Australia.

The Australian Institute of Health and Welfare report The definition, incidence and prevalence of acquired brain injury in Australia 1999 concluded "This review of definitions of ABI and estimates of its incidence and prevalence overseas and in Australia has shown that there is a good deal of uncertainty in the field."

Nonetheless some broad observations (1999) are:

These rates vary by gender, age and location.

For example hospital separations for TBI varied from 71 per 100,000 in the ACT to 211 per 100,00 in Queensland.

While in the table above there are much lower rates of Anoxic brain injury and Alcohol related brain injury and Brain damage present at birth or arising in early childhood this does not necessarily mean that these latter subgroups of ABI are insignificant in comparisons with stroke, TBI and ABI caused by degenerative conditions as some subgroups of ABI are not readily identified in the hospital system.

The Australian Institute of Health and Welfare Bulletin 55 Disability in Australia: Acquired Brain Injury, December 2007 states (pages 1 & 2):

Based on analyses of the Australian Bureau of Statistics' (ABS) 2003 Survey of Disability, Ageing and Carers:

• ABI is common: around 1 in 45 Australians (432,700 people) had ABI with activity limitations or participation restrictions due to disability. Almost three-quarters of these people were aged less than 65 years
• about 20,000 children aged under 15 years had ABI
• ABI was the main disabling condition reported by about 27,300 people aged under 65 years. A traffic injury was the main cause for more than half (55%) of these people
• more than one in three people with ABI aged under 65 years needed help with cognitive and/or emotional tasks.
• ABI caused by a traumatic event, such as a traffic accident or blow to the head, is referred to as traumatic brain injury. According to hospital records there were almost 21,800 hospital stays relating to traumatic brain injury in 2004–05

Hospitalisations for traumatic brain injury

The Australian Institute of Health and Welfare Bulletin 55 also states (page 10):

In 2004–05 there were almost 21,800 hospital stays for which a diagnosis associated with TBI was
recorded as either the principal or an additional diagnosis (Table A5)—a rate of 107 TBI-related
hospital stays per 100,000 people in the population.

(Note: It is not possible to use hospital data to say how many new incidences of traumatic brain injury (TBI)
there are in a given year because:
1. not all people who suffer a traumatic brain injury are hospitalised
2. people who are hospitalised more than once for their TBI will be counted more than once.)

The following chart shows the rate of hospitalisations for traumatic brain injury per 100,000 by age and gender.

Alzheimer's disease is the most common cause of ABI from degenerative diseases.

Stroke

About 48,000 people have a stroke in Australia each year and about one third of those have already had a stroke. More women are affected by stroke than men, due to the larger number of elderly women in the population. However, the age-standardised stroke incidence rate for men is 30% higher than for women. Strokes normally occur in older people aged 65 years or over, but around one in every five strokes happens to a person aged under 55.