Coronary heart disease and stroke mortality trends in Australia and New Zealand: comparison of official national mortality data and Global Burden of Disease estimates.

Background: Recent Global Burden of Disease (GBD) estimates show increasing cardiovascular disease (CVD) mortality in Australia and New Zealand, prompting concern. This study investigates whether such increases are observed in official national data.

Methods: Annual age-standardized coronary heart disease (CHD) and stroke mortality rates for ages 35-84 years in Australia/New Zealand from 2008 to 2018/19 were calculated using official national data and published GBD estimates. Differences in annual mortality rate percentage changes between official data and GBD estimates were calculated separately for each country. Joinpoint regression identified temporal trend changes.

Results: Official data showed annual decreases in CHD mortality of 4.9% (95% CI: 4.4%-5.5%) for Australia and 4.2% (3.7%-4.7%) for New Zealand on average; corresponding annual stroke mortality reductions were 4.3% (3.2%-5.3%) for Australia and 3.7% (2.9%-4.5%) for New Zealand. Absolute CHD mortality rates from GBD were substantively higher than from official data (e.g. 104.7 [103.0-106.5] vs 99.0 [97.3-100.7] per 100 000 people, respectively, Australia, 2008). Contrasting with ongoing declining rates using official data, GBD estimates showed slower overall mortality rate declines, recent increases in CHD mortality (e.g. 1.2% [0.2%-2.2%] annual increases from 2016 to 2019 for Australia), and stagnating stroke mortality. Differences are likely explained by GBD's redistribution of ill-defined causes of death and use of projected data after 2016, when national mortality data were unavailable for GBD estimates.

Conclusions: CHD and stroke mortality in Australia/New Zealand continue to decline, according to gold-standard official data. Disparities with GBD estimates highlight the need for transparency in reporting GBD methods and care in interpretation and application.