Demographic disparities in the incidence and case fatality of subarachnoid haemorrhage: an 18-year nationwide study from New Zealand.

Abstract

Background/Aims: Although the incidence and case-fatality of subarachnoid haemorrhage (SAH) vary within countries, few countries have reported nationwide rates, especially for multi-ethnic populations. We assessed the nationwide incidence and case-fatality of SAH in New Zealand (NZ) and explored variations by sex, district, ethnicity and time. Method(s): We used administrative health data from the national hospital discharge and cause-of-death collections to identify aneurysmal SAHs in NZ between 2001-2018. For validation, we compared these administrative data to those of two prospective Auckland Regional Community Stroke Studies. We subsequently estimated the incidence and case-fatality of SAH and calculated adjusted rate ratios (RR) with 95% confidence intervals to assess differences between sub-populations. Result(s): Over 78,187,500 cumulative person-years, we identified 5,371 SAHs (95% sensitivity and 85% positive predictive values) resulting in an annual age-standardised nationwide incidence of 8.2/100,000. In total, 2,452 (46%) patients died within 30 days after SAH. Compared to European/others, Maori had greater incidence (RR=2.23 (2.08-2.39)) and case-fatality (RR=1.14 (1.06-1.22)), whereas SAH incidence was also greater in Pacific peoples (RR=1.40 (1.24-1.59)) but lesser in Asians (RR=0.79 (0.71-0.89). By domicile, age-standardised SAH incidence varied between 6.3-11.5/100,000 person-years and case fatality between 40-57%. Between 2001-2018, the SAH incidence of NZ decreased by 34% and the case fatality by 12%. Conclusion(s): Since the incidence and case-fatality of SAH varies considerably between regions and ethnic groups, caution is advised when generalising findings from focused geographical locations for public health planning, especially in multi-ethnic populations.