There is limited evidence on the geographical variation in the prevalence of comorbidities in people with osteoarthritis in Alberta. Our study explores the spatial pattern of osteoarthritis comorbidities along the rural-urban continuum. The results showed a pattern of higher age-sex standardized prevalence rate of osteoarthritis comorbidities in the north and rural areas compared to the south and urban areas, respectively. Hot spots were identified in the north remote area for osteoarthritis with two or more comorbidities, and osteoarthritis with chronic obstructive pulmonary disease. This study provides information for health care planning to support access to health care services.
Osteoarthritis (OA) is the most common
form of arthritis affecting 10% to 15% of
Canadian population and is the leading
cause of hip and knee joint replacement
surgery
The Canadian Medical Association (CMA)
and Alberta Health Services (AHS) have a
goal to achieve equitable access to OA care,
with a focus on patients in rural and remote
areas
Records were extracted from five
administrative health databases - Alberta
Health Care Insurance Plan (AHCIP)
population registry, Discharge Abstract
Database (DAD), Physician Claims Database
(claims), Ambulatory Care Classification
System (ACCS), and Alberta National
Ambulatory Care Reporting System
(NACRS)
Based on the literature and expert guidance
from clinicians, we included a list of 8
chronic conditions for analysis:
hypertension (HTN), depression (DEP),
chronic obstructive pulmonary disease
(COPD), diabetes (DIAB), peripheral
vascular disease (PVD), cerebrovascular
disease (stroke) (CEVD), myocardial
infarction (MI), and congestive heart failure
(CHF). Validated algorithms for each of the
selected comorbid conditions were applied
to identify comorbidities
The OA cases were grouped by the number of comorbidities: OA with none of these comorbidities, OA with one of these comorbidities, OA with two or more of these comorbidities. With respect to the OA cases with only one comorbidity, we further categorized this group by the type of comorbidity: OA with only HTN, OA with only DEP, OA with only COPD, OA with only DIAB, OA with only CHF, OA with only PVD, OA with only MI, and OA with only CEVD.
The OA cases were stratified by sex and age
group (18-35, 35-44, 45-54, 55-65, 65-74,
75-85, and >=85 years of age). Direct
standardization method was applied to
calculate the age-sex standardized OA
comorbidity rates
Alberta Health Services created 5
geographic zones for directing operational
issues, and 7 rural-urban continuum for the
purposes of analysis and planning. The
rural-urban continuum were created based
on population density and distance from
urban centres, including Metro (Calgary and
Edmonton), Moderate Metro influence,
Urban (Grand Prairie, Fort McMurray, Red
Deer, Lethbridge and Medicine Hat),
Moderate Urban influence, Rural Centre
(Brooks, Canmore et al.), Rural, and Rural
Remote. By stratifying the rural-urban
continuum by the 5 geographic zones, we
identified 20 geographic sub-areas (Figure
1) in order to capture potential variation
associated with both zone and rural-urban
continuum
The latitude and longitude of each postal
code was obtained by linking the OA data
and the Postal Code Translator Files
We identified 359,638 OA cases in Alberta in 2013 (Table 1), of which 52% had at least one comorbidity (n=186,350), and 18% had two or more comorbidities (n=120,936). Comorbidities were more frequent in females in all comorbidity groups, compared to males (23% vs 20% for OA with at least one of these comorbidities; 8% vs 7% for OA with two or more comorbidities).
Among OA cases with only one comorbidity, HTN was the most frequent comorbid condition, accounting for 13% (n=46,871) of total OA cases, followed by DEP (10.6%, n=38,248), COPD (7%, n=25,495) and diabetes (2%, n=7,794). CHF, PVD, MI and CEVD were identified to be the least frequent comorbid conditions in OA cases, with the percentage of OA cases ranging from 0.3% for CHF to 0.04% for CEVD. Comorbidities with a frequency lower than 3% were excluded from spatial analysis due to limited number of cases.
By rural-urban continuum, the age-sex standardized prevalence rate for OA with one comorbidity ranged from 321 per 1,000 (Urban-North) to 269 per 1,000 (RuralCentre-North) and for OA with two or more comorbidities from 152 per 1,000 (Moderate Urban-North) to 263 per 1,000 (Rural Centre-South). For OA with HTN only, rates ranged from 101 per 1,000 (Rural-CentreCalgary) to 142 per 1,000 (Moderate-MetroCalgary), for DEP only 81 per 1,000 (RuralRemote-North) to 143 per 1,000 (RuralCentre-Calgary), and for COPD 61 per 1,000 (Rural-Centre-South) to 126 per 1,000 (Rural-Centre-North). In general, the prevalence rates for OA with comorbidities tend to be higher in the north, compared to OA without comorbidities (Figure 2). The rate of OA with HTN and OA with DEP was higher in the south. OA with COPD only was observed to be higher in the north.
Global Moran’s I suggested a statistically significant spatial autocorrelation for all comorbidity groups. A spatial weight matrix with a fixed distance of 6 km and at least 8 nearest neighbors was generated to model the spatial relationship of postal codes in both rural and urban areas. Hot spots analysis identified hot spots of OA with one comorbidity in both Rural-North and RuralSouth (Figure 3). OA with HTN showed hot spots in the Moderate Urban area, in both south and north, and Rural Remote – Northwest. While for OA with COPD only, we identified hot spots mostly in Rural Centre-North, Rural Remote –North, and Rural Remote –Northwest.
We explored the geographic variation in OA comorbidities and showed that higher rates of comorbidities in people with OA tend to be observed in the north rural areas. The findings provide valuable information for planning healthcare delivery and informing equitable access to health care. Further research will explore the driving factors influencing this observed variation.
Acknowledge funders.
This work was supported by the Canadian Institute of Health Research and the Arthur J.E. Child Chair in Rheumatology Research.