Estimating chronic disease prevalence
among the remote Aboriginal population of
the Northern Territory using multiple data
sources
Yuejen Zhao, Christine Connors, Jo Wright, Steve Guthridge
Department of Health and Families, Northern Territory
Ross Bailie
Menzies School of Health Research, Northern Territory
Abstract
Objective: To determine the prevalence rates of hypertension, diabetes, ischaemic
heart disease (IHD), renal disease and chronic obstructive pulmonary disease
(COPD), and their co-occurrence among the remote Aboriginal population of the
Northern Territory (NT) in 2005.
Methods: Information from a primary care chronic disease register (CDR) and
hospital inpatient database were linked to a population list by using a unique patient
identifier. A capture-recapture method (CRM) and multivariate log-linear models
were then applied to analyse the multiple datasets to estimate the prevalence
rates for the selected diseases and case ascertainment in each data source.
Results: The NT remote Aboriginal communities had considerably higher
prevalence rates across all five chronic diseases than national health survey
figures. At ages 50 years and over, the prevalence rates for hypertension and
renal disease were above 50%, diabetes 40%, COPD 30% and IHD above 20%.
In terms of data completeness, CDR and hospital sources were both relatively
incomplete, generally around 20−60%. The most common co-occurrences for
the five chronic diseases were between hypertension, diabetes, IHD and renal
disease.
Conclusions and implications: The prevalence rates calculated using this
method are comparable to estimates from rigorous small area studies, but are
markedly higher than those from single clinical data sources. The results indicate
that there is a considerable underdiagnosis of preventable chronic diseases in the
Aboriginal communities.
Keywords: Prevalence, data collection, epidemiology, chronic diseases,
Indigenous health services
For preventive and early intervention strategies for chronic disease
management to be effective, it is central to have reliable information about
the pattern of disease and exposures to major risk factors. This requirement is not
limited to one-off or intermittent estimates, but extends to systematic monitoring and
surveillance of the conditions to inform ongoing management. The implementation
of systematic monitoring is particularly important among the Northern Territory
(NT) Aboriginal population for whom noncommunicable diseases are estimated to
contribute 77% of the life expectancy gap between Aboriginal and non-Aboriginal
populations.1 The importance of chronic diseases management has prompted a
comprehensive NT intervention strategy, with a focus on five preventable chronic
diseases (PCDs) – hypertension, diabetes, ischaemic heart disease (IHD), renal
disease and chronic obstructive pulmonary disease (COPD).2 These five conditions
are
also significant in the broader Australian
population and make up 22% of national
burden of disease.3 The five conditions share
several underlying characteristics. They are
commonly developed at working age after
latent exposure to a limited number of core
risk factors including poverty, childhood
malnutrition, systemic infections, tobaccosmoking, alcohol abuse, poor access to
fruit and vegetables, obesity and physical
inactivity. The conditions are characterised
as being preventable, costly to manage and
rarely curable. They also have an uncertain
time of onset, are of prolonged duration and
are complicated by acute manifestations.
In the NT, the acute manifestations of
the five conditions consume 40-56% of
public hospital resource4 and result in pain,
disability and premature death for many
Territorians. There are also substantial
indirect costs through the impact on quality
of social and family life, and work-related
productivity.
Despite national efforts to collate existing
health survey, hospital morbidity and
mortality data, there remains a paucity of
relevant epidemiological information on
prevalence, incidence and survival rates
of the chronic diseases, particularly at a
regional level.5 Existing electronic, clinical
datasets remain an under-utilised option,
with only sporadic reports on the prevalence
rates of selected preventable chronic diseases
among Indigenous Australians. The existing
estimates have been based on singlesource
data and have generally focused
on diabetes,6-8 hypertension,9,10 and renal
diseases.11,12 Recent reports have combined
these as the metabolic syndrome related
conditions.13-15 Less is known about current