Surveys of microsatellite variation show that genetic diversity has largely recovered in two reef-building corals, Pocillopora damicornis and Seriatopora hystrix (Scleractinia: Pocilloporidae), on reefs which were decimated by the eruption of the volcano Krakatau in 1883. Assignment methods and gene flow estimates indicate that the recolonization of Krakatau occurred mainly from the closest upstream reef system, Pulau Seribu, but that larval input from other regions has also occurred. This pattern is clearer in S. hystrix, which is traditionally the more dispersal-limited species. Despite these observed patterns of larval dispersal, self-recruitment appears to now be the most important factor in supplying larvae to coral populations in Krakatau. This suggests that the colonization of devastated reefs can occur quickly through larval dispersal; however, their survival requires local sources of larvae for self-recruitment. This research supports the observation that the recovery of genetic diversity in coral reef animals can occur on the order of decades and centuries rather than millennia. Conservation measures aimed at sustaining coral reef populations in Krakatau and elsewhere should include both the protection of upstream source populations for larval replenishment should disaster occur as well as the protection of large adult colonies to serve as local larval sources.

Background

Insufficient data exist on population-based trends in morbidity and mortality to determine the success of prevention strategies and improvements in health care delivery in stroke. The aim of this study was to determine trends in incidence and outcome (1-year mortality, 28-day case-fatality) in relation to management and risk factors for stroke in the multi-ethnic population of Auckland, New Zealand (NZ) over 30-years.

Methods

Four stroke incidence population-based register studies were undertaken in adult residents (aged ≥15 years) of Auckland NZ in 1981-1982, 1991-1992, 2002-2003 and 2011-2012. All used standard World Health Organization (WHO) diagnostic criteria and multiple overlapping sources of case-ascertainment for hospitalised and non-hospitalised, fatal and non-fatal, new stroke events. Ethnicity was consistently self-identified into four major groups. Crude and age-adjusted (WHO world population standard) annual incidence and mortality with corresponding 95% confidence intervals (CI) were calculated per 100,000 people, assuming a Poisson distribution.

Results

5400 new stroke patients were registered in four 12 month recruitment phases over the 30-year study period; 79% were NZ/European, 6% Māori, 8% Pacific people, and 7% were of Asian or other origin. Overall stroke incidence and 1-year mortality decreased by 23% (95% CI 5%-31%) and 62% (95% CI 36%-86%), respectively, from 1981 to 2012. Whilst stroke incidence and mortality declined across all groups in NZ from 1991, Māori and Pacific groups had the slowest rate of decline and continue to experience stroke at a significantly younger age (mean ages 60 and 62 years, respectively) compared with NZ/Europeans (mean age 75 years). There was also a decline in 28-day stroke case fatality (overall by 14%, 95% CI 11%-17%) across all ethnic groups from 1981 to 2012. However, there were significant increases in the frequencies of pre-morbid hypertension, myocardial infarction, and diabetes mellitus, but a reduction in frequency of current smoking among stroke patients.

Conclusions

In this unique temporal series of studies spanning 30 years, stroke incidence, early case-fatality and 1-year mortality have declined, but ethnic disparities in risk and outcome for stroke persisted suggesting that primary stroke prevention remains crucial to reducing the burden of this disease.

BACKGROUND: Reliable data on trends of stroke incidence and outcomes over time are necessary for assessing the effectiveness of public health and clinical strategies, and for allocating healthcare resources. We assessed the levels and trends in incidence, mortality, early case fatality and disability for stroke in a defined, ethnically mixed population over 40 years. METHODS: To analyse data from five population-based stroke incidence studies in adult residents (age ≥15 years) of the Greater Auckland Region of New Zealand (NZ) (1.35 million) over 12-month calendar periods for 1981-1982, 1991-1992, 2002-2003, 2011-2012, and 2021-2022. Fatal and non-fatal, hospitalised and non-hospitalised stroke events (first-ever and recurrent) were identified through multiple overlapping sources using clinical World Health Organization (WHO) diagnostic criteria and neuroimaging to define three major pathological types of stroke: ischaemic stroke (IS), primary intracerebral haemorrhage (PICH), subarachnoid haemorrhage (SAH), and stroke of undetermined type (SUT). Crude and age-standardised annual incidence, mortality, 28-day case fatality and disability level, and 40-year trends were calculated by age, sex, and ethnicity assuming a Poisson distribution. For comparison of our findings, we carried out a pooled analysis of methodologically comparable population-based stroke epidemiology estimates in high-income countries over the last two decades. FINDINGS: Overall, there were 7462 first-ever strokes (9917 events) over the 40-year period (4,682,012 person-years). From 1981-1982 to 2021-2022, age-standardised stroke incidence rates decreased from 156/100,000 (95% confidence interval [CI] 143; 170) to 124/100,000 (119; 130) and mortality rates from 98/100,000 (88; 110) to 28/100,000 (26; 31) in nearly all age, sex, and ethnic groups. Moreover, from 2002-2003 to 2021-2022, there was an increase in stroke incidence of 1.28% per year (95% CI 0.38-2.17) in people aged 15-54 years, with the mean age of people with stroke decreasing from 73.0 (SD ± 13.8) in 2002-2003 to 71.6 (SD ± 14.9) in 2011-2012 and 70.7 (SD ± 15.2) years in 2021-2022 (p for trend <0.0001). The risk of stroke in Māori and Pacific people in 2021-2022 was almost 1.5 and 2.0 times greater than that in NZ Europeans. Ethnic disparities in the risk of stroke and age of stroke onset remained stable over the study period. From 1981-1982 to 2021-2022, 28-day stroke case fatality declined from 33.1% to 12.1% (p < 0.0001). There was a trend towards reducing 28-day case-fatality (from 31.6% [95% CI 27.6; 35.7] in 1981-1982 to 11.4% [10.0; 12.7] in 2021-2022) and an increasing proportion of stroke survivors with good functional outcome at discharge/28-days post-stroke (increased from 45.7% (95% CI 41.3; 50.0) in 1981-1982 to 60.2% (58.1; 62.3) in 2021-2022). INTERPRETATION: Stroke incidence, 1-year mortality and 28-day case-fatality and disability have decreased in Auckland, NZ over the last 4 decades. However, over the last decade (2011-2022) there was a stagnation in the decline in the age-standardised stroke incidence rates. The absolute numbers of people with strokes, and those who have died or remained disabled from stroke, have significantly increased from 1981 to 2022. Ethnic disparities in the risk and burden of stroke persist. Effective prevention strategies for stroke must remain a high priority. FUNDING: Health Research Council of New Zealand.