Excess mortality rates for estimating the non-fatal burden of stroke in Western Australia: a data linkage study

Non-fatal stroke burden measured in Years Lived with Disability (YLD) requires valid estimates of stroke case fatality to allow modelling of disease duration. In the model, case fatality can be calculated from the absolute risk of mortality in cases in excess of that in the non-diseased.

Our purpose was to estimate excess mortality rates in 28-day survivors of stroke in Western Australia and to evaluate differentials in survival by stroke type, age and time since the first stroke event.

Excess mortality among prevalent (first-ever plus existing) survivors was estimated from linked hospital and mortality data. Changes in excess mortality over time were calculated over a 6-year period.

Excess mortality increased with age for both males (21 per 1,000 in the 15- to 54-year to 109 per 1,000 in the > or =85-year age group) and females (16 and 122 per 1,000 for the 15- to 54-year and > or =85-year groups, respectively). Survival by stroke sub-types differed at ages <55 years but not >55 years. During the first year excess mortality was markedly higher, after which it was relatively constant for each age group. The assumption of constant rather than changing excess mortality in 28-day survivors of stroke had minimal effect on estimates of duration.

Measures of excess mortality in prevalent survivors have not previously been available for estimating YLD for stroke. An analysis of all stroke types combined is not likely to substantially bias estimates of non-fatal stroke burden nor is an assumption of constant excess mortality for survivors.