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Australian Health Review Australian Health Review Society
Journal of the Australian Healthcare & Hospitals Association
RESEARCH ARTICLE

Assessing improvements in survival for stroke patients in the Northern Territory 1992–2013: a marginal structural analysis

Yuejen Zhao A C , John Condon A B , Jiqiong You A , Steven Guthridge A and Vincent He B
+ Author Affiliations
- Author Affiliations

A Health Gains Planning, NT Department of Health, PO Box 40596, Casuarina, NT 0811, Australia. Email: jiqiong.you@nt.gov.au; steve.guthridge@nt.gov.au

B Menzies School of Health Research, PO Box 41096, Casuarina, NT 0811, Australia. Email: John.Condon@menzies.edu.au; Vincent.He@menzies.edu.au

C Corresponding author. Email: yuejen.zhao@nt.gov.au

Australian Health Review 39(4) 437-443 https://doi.org/10.1071/AH14146
Submitted: 3 June 2014  Accepted: 25 November 2014   Published: 23 February 2015

Abstract

Objective The aim of the present study was to investigate changes in stroke survival among Indigenous and non-Indigenous patients in the Northern Territory (NT).

Methods A longitudinal study was undertaken of stroke patients admitted to NT public hospitals between 1992 and 2013. The Kaplan–Meier method and proportional hazards regression were used for survival analysis. A marginal structural model was applied to adjust for time-dependent confounders and informative censoring.

Results There were 4754 stroke in-patients over the period, with 3540 new cases and 837 stroke deaths. Mean age of onset for Indigenous patients (51.7 years) was 12.3 years younger than that for non-Indigenous patients. After adjustments for confounders and loss to follow-up, in-hospital deaths were more likely among Indigenous patients (hazard ratio (HR) = 1.56; P < 0.01) and less likely among males (HR = 0.86; P < 0.05) and patients from remote areas (HR = 0.72; P < 0.01). There was a 3% decrease annually in mortality hazard from 1992 to 2013. Renal disease, cancer and chronic obstructive pulmonary disease had deleterious effects on stroke survival.

Conclusions Stroke survival has improved in the NT over the past two decades. The marginal structural models provide a powerful methodological tool that can be applied to hospital administrative data to assess changes in quality of care and the impact of interventions.

What is known about the topic? Stroke-related mortality has fallen in the past 30 years in Australia. Indigenous Australians have much worse health outcomes than other Australians, including higher stroke incidence and mortality, but it is not known whether stroke survival has improved for Indigenous stroke patients.

What does this paper add? This study measured long-term survival for Indigenous and non-Indigenous patients after hospital admissions for stroke care, using hospital admission data analysed by marginal structural models. The present study demonstrates the usefulness of this approach to the quality assessment of health care interventions.

What are the implications for practitioners? Hospital administrative data can, and should, be routinely used for monitoring long-term outcomes of acute care. Although survival has improved for Indigenous stroke patients over the past two decades, their survival remains lower than that of non-Indigenous patients. Coordinated acute and primary care plays a vital role in management of chronic diseases to improve stroke survival.


References

[1]  Kumar P, Clark ML. Clinical medicine. London: Elsevier Health Sciences UK; 2012.

[2]  World Health Organization (WHO). The atlas of heart disease and stroke. Geneva: WHO; 2004.

[3]  Organization For Economic Cooperation and Development (OECD). Health at a glance 2011: OECD indicators. Paris: OECD Publishing; 2011.

[4]  Australian Bureau of Statistics (ABS). Causes of death, Australia, 2012. Canberra: ABS; 2013.

[5]  Begg S, Vos T, Barker B, Stevenson C, Stanley L, Lopez A. The burden of disease and injury in Australia 2003. Brisbane: Australian Institute of Health and Welfare; 2007.

[6]  Johnston SC, Mendis S, Mathers CD. Global variation in stroke burden and mortality: estimates from monitoring, surveillance, and modelling. Lancet Neurol 2009; 8 345–54.
Global variation in stroke burden and mortality: estimates from monitoring, surveillance, and modelling.Crossref | GoogleScholarGoogle Scholar | 19233730PubMed |

[7]  Islam MS, Anderson CS, Hankey GJ, Hardie K, Carter K, Broadhurst R, Jamrozik K. Trends in incidence and outcome of stroke in Perth, Western Australia during 1989 to 2001: the Perth community stroke study. Stroke 2008; 39 776–82.
Trends in incidence and outcome of stroke in Perth, Western Australia during 1989 to 2001: the Perth community stroke study.Crossref | GoogleScholarGoogle Scholar | 18239179PubMed |

[8]  Australian Institute of Health and Welfare (AIHW). Stroke and its management in Australia: an update. Canberra: AIHW; 2013.

[9]  Thrift AG, Dewey HM, Macdonell RA, McNeil JJ, Donnan GA. Incidence of the major stroke subtypes initial findings from the North East Melbourne stroke incidence study (NEMESIS). Stroke 2001; 32 1732–8.
Incidence of the major stroke subtypes initial findings from the North East Melbourne stroke incidence study (NEMESIS).Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3MvktVagtA%3D%3D&md5=b777a6d1454c695abeb820ba8ec28aeaCAS | 11486098PubMed |

[10]  Hardie K, Jamrozik K, Hankey GJ, Broadhurst RJ, Anderson C. Trends in five-year survival and risk of recurrent stroke after first-ever stroke in the Perth Community Stroke Study. Cerebrovasc Dis 2005; 19 179–85.
Trends in five-year survival and risk of recurrent stroke after first-ever stroke in the Perth Community Stroke Study.Crossref | GoogleScholarGoogle Scholar | 15644631PubMed |

[11]  Australian Institute of Health and Welfare (AIHW). Life expectancy and mortality of Aboriginal and Torres Strait Islander people. Canberra: AIHW; 2011.

[12]  Katzenellenbogen JM, Vos T, Somerford P, Begg S, Semmens JB, Codde JP. Burden of stroke in Indigenous Western Australians. A study using data linkage. Stroke 2011; 42 1515–21.
Burden of stroke in Indigenous Western Australians. A study using data linkage.Crossref | GoogleScholarGoogle Scholar | 21493909PubMed |

[13]  Thrift AG, Hayman N. Aboriginal and Torres Strait Islander peoples and the burden of stroke. Int J Stroke 2007; 2 57–9.
Aboriginal and Torres Strait Islander peoples and the burden of stroke.Crossref | GoogleScholarGoogle Scholar | 18705992PubMed |

[14]  Tummala S. A multifactorial model of stroke and a comparison of the causality of stroke in Indigenous and non-Indigenous Australians. Cross-sections, The Bruce Hall Academic J 2012; 8 81–95.

[15]  Kilkenny MF, Harris DM, Ritchie EA, Price C, Cadilhac DA. Hospital management and outcomes of stroke in Indigenous Australians: evidence from the 2009 acute care national stroke audit. Int J Stroke 2013; 8 164–71.
| 22299773PubMed |

[16]  Byron P, Zhao Y, Guthridge SL, Brailsford R, Stacey F, Parkinson J. Medicare and Pharmaceutical Benefits Scheme usage patterns in the Northern Territory 1993/94 to 2003/04. Darwin: Department of Health and Community Services; 2005.

[17]  Australian Bureau of Statistics (ABS). Population characteristics, Aboriginal and Torres Strait Islander Australians. Canberra: ABS; 2010.

[18]  Foley M, Zhao Y, Condon J. Demographic data quality assessment for Northern Territory public hospitals, 2011. Darwin: NT Government; 2012.

[19]  Cadilhac DA, Moss KM, Price CJ, Lannin NA, Lim J, Anderson CS, Bateman-Steel CR, Arabena K, Cheng AC, Woolnough E. Pathways to enhancing the quality of stroke care through national data monitoring systems for hospitals. Med J Aust 2013; 199 650–1.
Pathways to enhancing the quality of stroke care through national data monitoring systems for hospitals.Crossref | GoogleScholarGoogle Scholar | 24237082PubMed |

[20]  Australian Government Department of Health and Ageing. The national evaluation of the second round of Coordinated Care Trials: final report. Coordination of care and efficiency of healthcare: Lessons from the second round of Australian Coordinated Care Trials. Part 1: executive summary. Canberra: Commonwealth of Australia; 2007.

[21]  Rosewarne C, Boffa J. An analysis of the primary health care access program in the Northern Territory: a major Aboriginal health policy reform. Aust J Primary Health 2004; 10 89–100.
An analysis of the primary health care access program in the Northern Territory: a major Aboriginal health policy reform.Crossref | GoogleScholarGoogle Scholar |

[22]  Kokotailo RA, Hill MD. Coding of stroke and stroke risk factors using international classification of diseases, revisions 9 and 10. Stroke 2005; 36 1776–81.
Coding of stroke and stroke risk factors using international classification of diseases, revisions 9 and 10.Crossref | GoogleScholarGoogle Scholar | 16020772PubMed |

[23]  Klein JP, Moeschberger ML. Survival analysis: techniques for censored and truncated data. New York: Springer; 2003.

[24]  Robins JM, Hernan MA, Brumback B. Marginal structural models and causal inference in epidemiology. Epidemiology 2000; 11 550–60.
Marginal structural models and causal inference in epidemiology.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3M%2FntlSnsw%3D%3D&md5=9ea00591e116b2d80311dee6954c97f7CAS | 10955408PubMed |

[25]  Bryan JF, Yu Z, van der Laan MJ. Analysis of longitudinal marginal structural models. Biostatistics 2004; 5 361–80.
Analysis of longitudinal marginal structural models.Crossref | GoogleScholarGoogle Scholar |

[26]  Faries DE, Kadziola ZA. Analysis of longitudinal observational data using marginal structural models. In Faries DE, Leon AC, Haro JM, Obenchain RL, editors. Analysis of observational health care data using SAS. Cary: SAS Institute; 2010. pp. 211–29.

[27]  Hernán MÁ, Brumback B, Robins JM. Marginal structural models to estimate the causal effect of zidovudine on the survival of HIV-positive men. Epidemiology 2000; 11 561–70.
Marginal structural models to estimate the causal effect of zidovudine on the survival of HIV-positive men.Crossref | GoogleScholarGoogle Scholar | 10955409PubMed |

[28]  StataCorp LP. Stata survival analysis and epidemiological tables reference manual. Texas: Stata Press; 1985.

[29]  Katzenellenbogen JM, Vos T, Somerford P, Begg S, Semmens JB, Codde JP. Excess mortality rates for estimating the non-fatal burden of stroke in Western Australia: a data linkage study. Cerebrovasc Dis 2010; 30 57–64.
Excess mortality rates for estimating the non-fatal burden of stroke in Western Australia: a data linkage study.Crossref | GoogleScholarGoogle Scholar | 20484903PubMed |

[30]  Reeves MJ, Bushnell CD, Howard G, Gargano JW, Duncan PW, Lynch G, Khatiwoda A, Lisabeth L. Sex differences in stroke: epidemiology, clinical presentation, medical care, and outcomes. Lancet Neurol 2008; 7 915–26.
Sex differences in stroke: epidemiology, clinical presentation, medical care, and outcomes.Crossref | GoogleScholarGoogle Scholar | 18722812PubMed |

[31]  Appelros P, Stegmayr B, Terént A. A review on sex differences in stroke treatment and outcome. Acta Neurol Scand 2010; 121 359–69.
A review on sex differences in stroke treatment and outcome.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BC3crpslCjtA%3D%3D&md5=950c076974d319c61bf7741653638ac8CAS | 20002005PubMed |

[32]  Appelros P, Stegmayr B, Terént A. Sex differences in stroke epidemiology: a systematic review. Stroke 2009; 40 1082–90.
Sex differences in stroke epidemiology: a systematic review.Crossref | GoogleScholarGoogle Scholar | 19211488PubMed |

[33]  Yusuf S, Reddy S, Ôunpuu S, Anand S. Global burden of cardiovascular diseases part II: variations in cardiovascular disease by specific ethnic groups and geographic regions and prevention strategies. Circulation 2001; 104 2855–64.
Global burden of cardiovascular diseases part II: variations in cardiovascular disease by specific ethnic groups and geographic regions and prevention strategies.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3MnoslSntA%3D%3D&md5=ae5e74be5a84a318b1097bd421ea65cdCAS | 11733407PubMed |

[34]  Cadilhac D, Kilkenny M, Longworth M, Pollack M, Levi C. Metropolitan–rural divide for stroke outcomes: do stroke units make a difference? Intern Med J 2011; 41 321–6.
Metropolitan–rural divide for stroke outcomes: do stroke units make a difference?Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BC3MrnvVehsw%3D%3D&md5=6d275dec1556d03fb2541ee73a7e1380CAS | 20546059PubMed |

[35]  Lee AH, Somerford PJ, Yau KK. Factors influencing survival after stroke in Western Australia. Med J Aust 2003; 179 289–93.
| 1:CAS:528:DC%2BD3sXotlyku7w%3D&md5=7f56e1e8f169f6fd2d72296ce5b84538CAS | 12964910PubMed |

[36]  Zhao Y, Condon JR, Guthridge S, You J. Living longer with a greater health burden: changes in the burden of disease and injury in the Northern Territory Indigenous population between 1994–1998 and 1999–2003. Aust N Z J Public Health 2010; 34 S93–8.
Living longer with a greater health burden: changes in the burden of disease and injury in the Northern Territory Indigenous population between 1994–1998 and 1999–2003.Crossref | GoogleScholarGoogle Scholar | 20618304PubMed |

[37]  Zhao Y, Goss J, Malyon R. What drives health spending in the Northern Territory? Economic Papers 2010; 29 292–300.
What drives health spending in the Northern Territory?Crossref | GoogleScholarGoogle Scholar |

[38]  Lawes CM, Hoorn SV, Rodgers A. Global burden of blood-pressure-related disease, 2001. Lancet 2008; 371 1513–18.
Global burden of blood-pressure-related disease, 2001.Crossref | GoogleScholarGoogle Scholar | 18456100PubMed |

[39]  Brønnum-Hansen H, Davidsen M, Thorvaldsen P. Long-term survival and causes of death after stroke. Stroke 2001; 32 2131–6.
Long-term survival and causes of death after stroke.Crossref | GoogleScholarGoogle Scholar | 11546907PubMed |

[40]  Toschke AM, Gulliford MC, Wolfe CD, Rudd AG, Heuschmann PU. Antihypertensive treatment after first stroke in primary care: results from the general practitioner research database. J Hypertens 2011; 29 154–60.
Antihypertensive treatment after first stroke in primary care: results from the general practitioner research database.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXhsFGku7bK&md5=8e7540c1108b6ac32e4fad44a4054fb8CAS | 20842045PubMed |

[41]  Lee S, Shafe AC, Cowie MR. UK stroke incidence, mortality and cardiovascular risk management 1999–2008: time-trend analysis from the General Practice Research Database. BMJ Open 2011; 1 e000269
UK stroke incidence, mortality and cardiovascular risk management 1999–2008: time-trend analysis from the General Practice Research Database.Crossref | GoogleScholarGoogle Scholar | 22021893PubMed |

[42]  Shi L, Macinko J, Starfield B, Xu J, Politzer R. Primary care, income inequality, and stroke mortality in the United States: a longitudinal analysis, 1985–1995. Stroke 2003; 34 1958–64.
Primary care, income inequality, and stroke mortality in the United States: a longitudinal analysis, 1985–1995.Crossref | GoogleScholarGoogle Scholar | 12843344PubMed |

[43]  Heeley EL, Wei JW, Carter K, Islam MS, Thrift AG, Hankey GJ, Cass A, Anderson CS. Socioeconomic disparities in stroke rates and outcome: pooled analysis of stroke incidence studies in Australia and New Zealand. Med J Aust 2011; 195 10–14.
| 21728934PubMed |

[44]  Pepper EM, Cadilhac DA, Pearce DC, Burrow J, Weeramanthri TS. Stroke among Indigenous Australians at Royal Darwin Hospital, 2001–02. Med J Aust 2006; 184 195
| 16489908PubMed |

[45]  Ariesen M, Claus S, Rinkel G, Algra A. Risk factors for intracerebral hemorrhage in the general population a systematic review. Stroke 2003; 34 2060–5.
Risk factors for intracerebral hemorrhage in the general population a systematic review.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3szmtFektQ%3D%3D&md5=436c22ddebc211ed63bb53e06a45fa59CAS | 12843354PubMed |

[46]  Cole SR, Hernán MA, Robins JM, Anastos K, Chmiel J, Detels R, Ervin C, Feldman J, Greenblatt R, Kingsley L. Effect of highly active antiretroviral therapy on time to acquired immunodeficiency syndrome or death using marginal structural models. Am J Epidemiol 2003; 158 687–94.
Effect of highly active antiretroviral therapy on time to acquired immunodeficiency syndrome or death using marginal structural models.Crossref | GoogleScholarGoogle Scholar | 14507605PubMed |

[47]  Teng M, Wolf M, Ofsthun MN, Lazarus JM, Hernán MA, Camargo CA, Thadhani R. Activated injectable vitamin D and hemodialysis survival: a historical cohort study. J Am Soc Nephrol 2005; 16 1115–25.
Activated injectable vitamin D and hemodialysis survival: a historical cohort study.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXjsVWqt70%3D&md5=c1dd9cc8ef7511e973bad6af12153000CAS | 15728786PubMed |

[48]  Cadilhac DA, Lannin NA, Anderson CS, Levi CR, Faux S, Price C, Middleton S, Lim J, Thrift AG, Donnan GA. Protocol and pilot data for establishing the Australian Stroke Clinical Registry. Int J Stroke 2010; 5 217–26.
Protocol and pilot data for establishing the Australian Stroke Clinical Registry.Crossref | GoogleScholarGoogle Scholar | 20536618PubMed |

[49]  Australian Bureau of Statistics (ABS). Census of population and housing: Socio-Economic Indexes for Areas (SEIFA), Australia, 2006. 2006. Available at: http://www.abs.gov.au/AUSSTATS/abs@.nsf/DetailsPage/2033.0.55.0012006?OpenDocument [verified 20 February 2014].