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| Journal of the New Zealand Medical Association,
30-January-2004, Vol 117 No 1188
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Regional variations in asthma hospitalisations among Maori
and non-Maori
Lis Ellison-Loschmann, Ron King and Neil Pearce
Although the prevalence of asthma is similar in Maori and
non-Maori children, Maori children and adults experience excess morbidity and
higher hospitalisation rates than non-Maori.1,2
The Maori Asthma Review concluded that asthma was more severe and that
hospitalisation and mortality rates for Maori exceeded those of non-Maori
primarily due to inadequate access to appropriate healthcare and asthma
education.3,4 It was suggested that these
problems of access might be particularly acute in rural areas. More generally,
there is widespread interest in regional differences and a common belief that
asthma prevalence may be higher in rural
areas.5
In fact, few studies have examined regional differences in
asthma prevalence or severity in New Zealand, and those that have been conducted
have found little evidence of regional differences. The New Zealand arm of the
International Study of Asthma and Allergies in Childhood (ISAAC) was conducted
in six New Zealand centres in 1992–1993.6
Three of these were urban (Auckland, Wellington, Christchurch) and three were
‘provincial’ (Bay of Plenty, Hawke’s Bay, Nelson). In general,
there were no regional differences in prevalence rates of asthma symptoms with
the possible exception of Nelson, which had slightly lower prevalence rates in
the 6–7 years age group.
Similar analyses for adults were conducted as part of the
New Zealand component of the European Community Respiratory Health Survey
(ECRHS).7,8 The 12-month-period prevalence of
asthma (defined as woken by shortness of breath, or an attack of asthma in the
past year, or current asthma medication) was 15.2% overall, but was 22.1% in
Maori, 20.6% in Pacific people and 14.3% in ‘others’ (this study in
adults therefore found a difference in asthma symptom prevalence between Maori
and non-Maori in contrast with previous studies in children, which have
generally found asthma prevalence to be similar in Maori and
non-Maori)1. The regional findings were not
presented separately for Maori and non-Maori. However, overall there was no
urban/rural difference in adult asthma prevalence: the prevalence of asthma was
15.5 % in urban areas, 14.7 % in provincial areas, and 13.8 % in rural areas. In
North Island electorates, the highest age- and ethnicity-standardised
prevalences were found in some of the electorates in the Auckland and Wellington
urban regions, although prevalence was also high in some rural electorates
including Raglan (18.0%), Horowhenua (18.4%) and Wairarapa (18.4%); the lowest
prevalences were found in other rural electorates including King Country (5.5%),
Matamata (10.1%) and Rotorua (10.3%). In South Island electorates, the highest
prevalences were found in the Christchurch and Dunedin urban areas, and the
lowest prevalences were again found in rural electorates including Clutha
(11.3%), Rangiora (9.5%), and Wallace (9.4%).
Thus, previous studies of asthma prevalence in New Zealand
children and adults show little evidence of systematic urban/rural differences
in asthma prevalence. The small differences that may exist involve slightly
lower prevalence in rural areas. However, these findings were not reported
separately for Maori and non-Maori, and were related to asthma prevalence rather
than severity. While they are imperfect measures of asthma morbidity,
hospitalisation and mortality rates do nonetheless provide important information
as markers of asthma severity, although it is possible that the level of
severity may still be underestimated. While these analyses examine regional and
ethnic differences in asthma hospitalisation rates we acknowledge that trends in
asthma admission rates are difficult to interpret, being dependent on asthma
severity, access to healthcare and individual patterns of medical
practice.2
MethodsCalculation
of Maori and non-Maori rates There are considerable problems in the
calculation of Maori health statistics, particularly when examining time trends,
because of changes in both the numerator and denominator information. These
issues have been reviewed in depth
elsewhere,2,9–12 but will be considered
briefly here. Prior to 1986, both deaths and census data were based on a
biological definition of Maori; from the 1986 Census the question became one of
self-identification, and for the 1986 and 1991 censuses the ‘sole
Maori’ definition is the most appropriate in calculating mortality and
hospitalisation rates because this provides reasonable consistency over
time.9,10 Changes to ethnicity recording for
death certificates in 1995, and further modification of the ethnicity question
in the 1996 Census mean that, for both numerator and denominator data, the
‘Maori ethnic group’ definition is most appropriate from 1996
onwards.11,12 These problems are less acute
when calculating hospitalisation rates, as in this study, since the methods of
recording ethnicity in hospitalisation data have not changed markedly during the
period under consideration. Furthermore, we are not examining time trends during
this period, but rather we are comparing hospitalisation rates in different
regions during this time period as a whole. Thus, problems in the classification
of ethnicity are likely to result in an underestimate of the overall relative
risk between Maori and non-Maori, but are less likely to affect the regional
comparisons within Maori and within non-Maori data.
Hospitalisation
data We studied asthma hospitalisations (defined here as the primary
diagnosis, ICD-9 code 493) in Maori and non-Maori during 1994–2000 using
the Ministry of Health filtered, publicly funded discharge data set (excludes
hospital transfers and duplicate records). For the reasons previously discussed,
census data using the ‘sole Maori’ definition have been used in the
calculation of the population totals and hospitalisation rates for 1994 and
1995, while the ‘Maori ethnic group’ definition is used for the
1996–2000 data set. There were only a small number of hospitalisations for
Pacific people in many areas, and therefore the Pacific data were excluded from
the analyses. Hence, the term ‘other’ refers to hospitalisation
rates for non-Maori/non-Pacific people.
Data analysis
We calculated hospitalisation rates for Maori and non-Maori in each of the 74
territorial local/land authorities (TLAs), commonly referred to as territorial
authorities (TAs). TAs were chosen as the area unit for analysis because these
provided reasonable numbers of hospitalisations, and it was possible to classify
them as urban or rural. The boundaries of TAs are defined according to
‘community of interest’ considerations including the relevance of
the community components to each other and the ability of the unit to
effectively service its community.13 The 74 TAs
comprise 15 cities and 59 districts. This classification provides a useful proxy
for urban versus rural populations. The term ‘urban’ relates to the
city authorities whose populations are predominantly urban; the term
‘rural’ relates to those district authorities that have the greatest
proportion of their population residing in rural and smaller urban
areas.
The TA-based hospitalisation rates are calculated using
the spatially aggregated hospitalisation records, which contain the
patients’ resident domicile codes (alternatively known as census area
units). However, there still remain some TAs where hospitalisation or
denominator numbers for particular age groups are too small to reliably
calculate. Any TAs with fewer than 15 counts for the 1994–2000 period are
designated on the maps (Figures 1 and 2) as ‘insufficient data’. The
15-count cut-off is due to the large increase in relative standard error
(>25% RSE) below this.
Analyses of deaths typically focus on the 5–34
age range, because of the difficulty in confirming asthma diagnoses for deaths
outside of these years.14 While the data are
reasonably accurate for asthma
hospitalisations15 we have focused on the
5–34 age group in presenting the findings although other age groupings
(0–4, 5–14, 15–34 and 35–74 years) were also analysed
and have been included. The software used for the mapping was Environmental
Systems Research Institute ArcView 3.2 desktop Geographic Information System.
The data were extracted from the NZHIS National Minimum Dataset using SAS 8 for
Windows.
ResultsEach of the TAs were ranked based on
asthma hospitalisation rates for Maori and non-Maori. Figure 1 shows the map of
5–34 year age-specific discharge rates (per 10 000 per year) for Maori by
TA. The highest rates were in Tauranga, Invercargill, Wanganui, South Wairarapa
and Gisborne; the lowest rates were in Rodney, Tasman, Franklin, Waitaki and
North Shore City. Figure 2 shows the corresponding patterns for non-Maori. Table
1 presents the number of admissions and hospitalisation rates for Maori and
non-Maori with the total rate, ranked from highest to lowest, for each TA (click here to view Table 1).
We also conducted regional analyses separately in Maori and
non-Maori for the 0–4, 5–14, 15–34 and 35–74 age groups
(not shown in the figures). For Maori the highest rates in the 0–4 age
group (per 10 000 per year) were in Invercargill (18.08), Tauranga (17.91),
Hastings (17.51), Masterton (17.49) and New Plymouth (15.84). In the 5–14
years age group, Invercargill (5.76), Wanganui (4.96), Queenstown Lakes (4.55)
and Gisborne (4.43) recorded the highest hospitalisation rates; for 15- to
34-year-olds, South Wairarapa (3.39), Kaikoura (3.27) and Tauranga (3.25) had
the highest rates; while Stratford (6.48), Central Hawke’s Bay (6.31) and
South Taranaki (5.21) had the highest asthma hospitalisation rates for the
35–74 years age group.
Figure 1. Maori 5–34 year age-specific asthma
discharge rates by territorial authority (1994–2000)
 Figure 2. Non-Maori 5–34 year age-specific asthma
discharge rates by territorial authority (1994–2000)
 Table 2 shows the findings (as age-specific rates per 10
000) grouped into urban and rural areas. In each age group the relative risk of
hospitalisation for Maori was higher in rural TAs than in urban TAs, whereas for
non-Maori overall the relative risk of hospitalisation was higher in urban than
in rural TAs.
Table 2. Hospitalisation rates by age and ethnicity for
rural/urban territorial authorities (per 10 000)
DiscussionWe have examined regional patterns
of asthma hospitalisations in Maori and non-Maori. There are some limitations to
the data that should be noted. First, as with our earlier paper examining time
trends in hospitalisation and mortality rates,2
the lack of standardised ethnicity data means that the monitoring of Maori
hospitalisation trends is not straightforward, although these problems are
unlikely to be of major concern when making regional comparisons during the same
time period. Second, the hospitalisation data represent episodes of care and may
include people who have been hospitalised on more than one occasion. Similarly,
many admissions in the age groups 0–4 years and 35 years or more that are
classified as asthma will be due to viral infections and chronic obstructive
pulmonary disease respectively. However, this factor is unlikely to have
significantly affected the regional patterns presented here.
These analyses confirm previous evidence that asthma
hospitalisation rates are higher in Maori than in
non-Maori,2 despite the fact that asthma
prevalence is similar in Maori and non-Maori
children.1 They further indicate that this
excess of hospitalisations is higher in rural than in urban areas, although the
difference in hospitalisation rates is not large. We found non-Maori
hospitalisation rates were generally higher in urban areas in contrast with the
pattern for higher rates in rural areas seen in the Maori population.
These findings are in contrast with previously published
data on regional differences in asthma
prevalence.6,7 The earlier studies showed
little or no urban/rural difference, and the small differences that did exist
appeared to involve slightly lower prevalences in rural areas. Thus, differences
in prevalence are unlikely to account for the higher asthma hospitalisation
rates for Maori in rural areas. This suggests that what we have observed
reflects differences in asthma exacerbation and disease severity. It is possible
that there may be some real differences in asthma prevalence between some TAs;
however, the evidence from this review indicates that there does not seem to be
any systematic urban/rural difference.
The Maori Asthma Review concluded that asthma was more
severe and that hospitalisation and mortality rates for Maori exceeded those of
non-Maori primarily because of inadequate access to appropriate healthcare and
asthma education.3,4 It was also reported that
these problems may be particularly severe in rural areas. At the individual
level, cost was a major factor related to access identified in the Maori Asthma
Review.3 Costs included travel to the
doctor’s surgery, doctor’s fees and prescription charges. These
costs might be further exacerbated for those living in isolated rural
communities. There was also strong support expressed in the Review for low-cost
health clinics, but only as a ‘second best’ option to the provision
of free primary healthcare. The introduction in 1997 of free consultations for
patients under six years old may have relieved some of the financial burden
associated with visits to GPs for this age
group.16 However, prescription costs for
medications remain a major issue and, obviously, there are significant numbers
of people with asthma who have been outside of the qualifying age parameter.
Similarly, in a 1998 study of 401 low-income households around New Zealand, 56%
of participants had not visited a doctor in the previous year because of cost
and 17% identified asthma as a condition that had gone untreated as a result of
this.17 GP consultation fees and prescription
charges have been under review as part of the Primary Health Care
Strategy.18
A study of access and utilisation of primary healthcare
amongst Maori and low-income New Zealanders, using data collected during
1994–1995, found cost to be a significant barrier in both population
groups, together with poor access to public transport and isolated populations
in rural settings.19 Overseas studies have
found that inaccessibility of acute hospital services may increase the risk of
asthma mortality.20 Geographic isolation and
limited public transport were documented in the Maori Asthma Review as being
significant factors for Maori in their decision making about accessing health
services. There was also the additional factor of cost associated with transport
for those living in rural or isolated areas, with very limited options available
in terms of public transport.3 The recently
announced funding for rural services by the Ministry of
Health21 will concentrate resources on
supporting and retaining primary healthcare teams currently working in rural
areas as well as provide for some national initiatives to be undertaken for
encouraging the recruitment of primary healthcare workers to rural areas on both
a short- and long-term basis.
In addition to issues of cost and geographic isolation, the
Maori Asthma Review identified differential management of asthma and inadequate
access to appropriate healthcare and asthma education as contributing to the
high asthma morbidity rate amongst Maori.3 One
study found that Maori were less likely to have an action plan and less likely
to use a peak flow meter. Relative to the severity of their asthma, Maori lost
more time from work or school and needed more hospital
services.22 A further study in Auckland found
that 33% of Polynesian children were not receiving any asthma drugs in the 24
hours prior to a hospital admission compared with 14% of European children. It
also found that fewer Maori children were taking preventive medications compared
with European children (13% vs 25%). The study concluded that rates of acute,
severe asthma, resulting in higher admission rates for Maori and Pacific
Islanders, were primarily due to differences in medical management. Issues such
as compliance and utilisation of services have been shown to be contributing
factors, but the major influence was that of the prescribing patterns of medical
practitioners.23 Similar conclusions have been
reached in subsequent studies, which propose that differences in asthma
morbidity, between Maori and non-Maori, are most likely related to differences
in access to, and delivery of, asthma care.1 It
is not clear whether these problems of asthma management are particularly acute
in rural areas. However, where Maori have been actively involved in the
planning, establishment and maintenance of rural, community-led asthma
self-management programmes, improved access to health services and reduced
asthma morbidity was seen.24,25
Passive exposure to tobacco smoke may contribute to the
increased hospital admissions seen in Maori children, although it is unlikely to
entirely explain the level of greater asthma severity reflected in hospital
admission rates.26 One New Zealand study of
adult asthma prevalence suggests that the increased frequency of symptoms
amongst adult Maori may in part be a reflection of greater non-allergenic
bronchial symptoms related to increased exposure to tobacco, both actively and
passively, compared with non-Maori.27
In summary, while we have found that there are rural/urban
differences in Maori and non-Maori asthma hospitalisation rates, these
differences are not large, and there are Maori/non-Maori differences within
urban areas as well as within rural areas. However, it is likely that the higher
asthma hospitalisation rates among Maori that we have observed reflect
differences in asthma exacerbation and disease severity as a result of reduced
access to asthma health services, which may be particularly acute for those
people living in rural areas.
Author information:
Lis Ellison-Loschmann, HRC Maori Health Research Training Fellow, Centre for
Public Health Research, Massey University; Ron King, Public Health Intelligence,
Ministry of Health, University of Auckland; Neil Pearce, Professor, Centre for
Public Health Research, Massey University, Wellington
Acknowledgements:
Lis Ellison-Loschmann is funded by a Training Fellowship in Maori Health
Research, and the Centre for Public Health Research is supported by a Core
Programme Grant from the Health Research Council. Thanks to Craig Wright at the
Ministry of Health for assisting with collating the data used in these
analyses.
Correspondence: Lis
Ellison-Loschmann, Centre for Public Health Research, Massey University
Wellington Campus, Private Box 756, Wellington. Fax: (04) 380 0600; email: l.ellison-loschmann@massey.ac.nz
References:
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