The current understanding of the international burden of diabetes-related complications is poor and there is paucity of data on a population level, for hospital mortality in Australian adults with diabetes. Using the national representative sample of more than 554000 adult admissions of people with and without diabetes from 2014-15 to 2016-17, our study provided the needed regional data on hospital outcomes of Australians living in the high-risk region of South Western Sydney.1, 6, 7 The study showed that over the three years, and across all ages, people with diabetes continue to have higher mortality rates compared with their counterparts without diabetes. The age standardised mortality rate among inpatients with diabetes was about three times higher than the general Australian population, and more in men than women, and this did not improve over time. Multivariable analyses revealed similarities in the drivers of mortality in both groups, with higher odds of death on admission in diabetes than the non-diabetes participants mostly in those aged 55 years and over, who were previously married, or stayed in hospital for more than 4 days and people who received intensive care during admission. Irrespective of the diabetes status, having a respiratory and circulatory system comorbidity should be considered a red flag in hospital, since it further increases their odds of death during admission.
The study showed for the first time that the standardized mortality among admitted people with diabetes in Australian public hospitals was significantly higher than the background population and remained so after three years. This finding was consistent with previous studies in non-admitted people.4 Harding et al’s study4 which used data from Australians who were registered on the National Diabetes Services Scheme between 1997 and 2010 but data was analysed based on diabetes type. They found that people with type 1 and type 2 diabetes experienced 3 and 1.2 times increased risk of all-cause mortality, respectively, over thirteen years.4 Without discriminating between diabetes type, Lind et al23 used a large diabetes population in Ontario, Canada to show that the diabetes mortality rate ratios decreased from 1.90 to 1.51 between 1996 and 2009 and decreased from 2.14 to 1.65 in a diabetes population from the U.K. Data presented from the National Survey of U.S. adult population with diabetes found that between 1997 and 2006, there was a decline of 23 and 40% in all-cause and CVD death rates respectively, which were similar between gender. 24 Allemann et al25 found that SMRs for people with type 1 and type 2 diabetes decreased significantly from 4.5 in 1974 to 3.5 in 2005 in Switzerland. The higher SMRs reported in their study25 compared to the present study may be related to the longer follow up periods and the fact that the previous studies were conducted when mortality from diabetes was much higher compared with the general population. In addition, the small differences with data from other studies discussed reflect differences in the populations.
This study found that men had higher mortality rate and were more likely to die in hospital compared with women, independent of the diabetes status. Mortality rates were 1.3 times as high for men as women (23.1 and 19.9 per 1,000 admitted people in SWS, respectively) and the likelihood of dying in hospital was still almost twice as high for men than women with diabetes. Consistent with our finding was the 1.7 times higher mortality rates in men than women reported in the recent Australian National survey data.1 However, Taylor et al found a higher relative risk of death in females with diabetes compared with their male counterparts in the UK (RR 2.47, 95%CI 2.23–2.72 versus RR 1.93, 95%CI 1.79–2.07),26 whereas among people with diabetes admitted electively to hospital, a higher additional risk of death was also found in females than males.8 In a cohort of US and Japanese participants with and without diabetes, Liu et al found a higher relative risk of mortality among US women with diabetes (HR 1.59 p = 0.01) but no difference was observed among male and females in Japan.27 In an Australian study using NDSS database, men showed higher excess risk of mortality than women.4 The mixed results demonstrated by the different studies, warrants further investigation into the association between sex and diabetes related mortality.
Europeans had lower hospitalisation but higher in hospital mortality rates compared with Australians and both had higher mortality rates than Pacific people. A previous report from the Australian Institute of Health and Welfare found similar higher mortality rates among Europeans than their Australian-born counterparts.28 Although, an increased prevalence of diabetes and associated complications would be expected to lead to more frequent hospitalisations it may not always correspond with high mortality rates.28 Low hospitalisation rates may also reflect poor management of diabetes complications rather than less complications.29 The fact that ethnicity remained a significant factor even after adjusting for all the potential covariates in the multivariate analysis, suggests that ethnicity plays an important role in diabetes related complications among inpatients.
Age and marital status were also associated with in-hospital mortality in people with and without diabetes even after adjustment for all potential covariates. Older age is a known risk factor for mortality.12 The higher odds of mortality among those who were widowed was consistent with previous studies30, 31 which found about 2.2 higher risk of all-cause mortality among those who were widowed compared with married people in Iran.30 This can be attributed to the findings from a meta-analysis that marriage or support from the spouse is associated with a reduction of up to 15% in the risk of all-cause mortality.31 Thus suggesting that marriage may have a health protective effect in reducing stress and anxieties and promoting positive healthy behaviours, while not being married may adversely affect the health of individuals.32 It has also been suggested that the emotional shock of losing a spouse and a lack of social support contributed to higher mortality rate in those who were widowed.33
The study found that participants who received intensive care during admission had the highest odds of in hospital mortality. This was similar to the findings of a systematic review and meta-analyses, which determined that diabetes is associated with an increased morality risk in cardiac surgery patients admitted to ICU34 and this may be related to the high blood glucose levels in ICU.33 Although at the time of this study, HbA1c has been recommended for use as a diagnostic test for diabetes in Australia,35 it was still not commonly performed during admission across SWSLHD hospitals particularly among older participants. 36
Similar to previous studies, 9–11, 26, 27 we found significant associations between comorbidities affecting the respiratory and circulatory systems and increased odds of death in people with and without diabetes. Although studies 9–11 significant associations between mortality and other comorbidities including cerebrovascular, renal and vascular diseases have been reported, these were not replicated in our study. The odds of death among admitted participants who reported these comorbidities was greater in the non-diabetes than the diabetes group in the univariate analysis. However, this discrepancy was reduced after adjusting for the covariates suggesting the overall poorer health outcomes in residents of South Western Sydney compared to NSW as a whole.7
The main strength of this study is that it is population based with a large sample size. Also, the use of place of residence rather than admitting hospital to define the population removes the bias associated with secondary/tertiary care centres, as well as including people admitted to hospitals outside the district. The main limitations of the study are due to the nature of the data being used (secondary data analysis). There are several limitations, however, that should be acknowledged. The APDC is an administrative database, and there are inherent limitations with using administrative databases for research purposes.37 There was no information about type of diabetes, country of birth was used instead of ethnicity, and indigeneity are not routinely available. Also, the use of de-identified data did not allow for the identification of multiple admissions, and data were not available for one of the seven LGAs in the District. No body mass index or glucose data was used in this study, and socioeconomic status data were also not available. Furthermore, data measures of diabetes severity which affect mortality risk, including duration of diabetes and glycaemic control were not available, and thus could not be adjusted for.38