Abstract
Objective To measure the incidence of poststreptococcal glomerulonephritis (PSGN) and resulting complications in northwestern Ontario, including among Indigenous and rural populations.
Design Cross-sectional study.
Setting As the only tertiary care hospital in northwestern Ontario, Thunder Bay Regional Health Sciences Centre (TBRHSC) functions as the primary referral centre for most of the region. The catchment population has substantial Indigenous (21.5%) and rural (34.2%) populations.
Participants All cases of PSGN managed at TBRHSC over an 8-year period from January 1, 2010, to December 31, 2017.
Main outcome measures Cases were classified as confirmed, probable, or possible based on the type of evidence available. Patients’ rurality and Indigenous status were recorded. Incidence rates and incidence rate ratios of all, pediatric (<18 years), and adult PSGN cases were calculated, as were incidence rates and incidence rate ratios of those requiring dialysis. Linear interpolation and extrapolation were used to estimate the population in non-census years.
Results Over the 8-year study period, 33 cases of PSGN were observed with annual incidence rates of 0.0 to 4.8 per 100,000 person-years and a mean annual incidence rate of 1.8 (95% CI 1.2 to 2.5) per 100,000 person-years. Of these 33 cases, 28 were confirmed with renal biopsy or clinical and laboratory data. Indigenous patients accounted for 61% (n=17) of confirmed cases and were 6.0 (95% CI 2.8 to 13, P<.001) times as likely to have PSGN and 9.6 (95% CI 3.0 to 31, P<.001) times as likely to require dialysis compared with non-Indigenous patients. Patients living in rural areas accounted for 71% (n=20) of confirmed cases and were 3.2 (95% CI 1.4 to 7.3, P=.006) times as likely to have PSGN and 3.9 (95% CI 1.0 to 10, P=.02) times as likely to require dialysis compared with patients in urban areas.
Conclusion The main burden of PSGN in northwestern Ontario occurs among Indigenous and rural populations. Additional research is required to investigate the true overall burden of PSGN in the region. In collaboration with regional Indigenous groups, advocacy is needed for PSGN to be made reportable and public health action must be taken to address these pronounced disparities.
Poststreptococcal glomerulonephritis (PSGN) is a nonsuppurative complication of group A streptococcal (GAS) infection and primarily a disease of social inequality.1 Globally, PSGN accounts for substantial morbidity and mortality in low-income settings but is relatively uncommon in higher-income countries.1,2 Among the latter, the main burden of PSGN has been documented among the Indigenous population in Australia, with rural and remote populations being affected in particular.1-4 The parallels between Indigenous populations in Canada and Australia are well described5; however, only recently has PSGN been identified as a public health concern in northwestern Ontario.6,7
Northwestern Ontario has unique demographic and geographic features that influence the health status of the region. At 526,000 km2 in size, the region accounts for approximately half of the province’s land area, but its population (235,900 as of 2018) represents less than 2% of the provincial total,8 with 34.2% considered to reside rurally.9 Indigenous people compose 21.5% of the population in northwestern Ontario compared with 2.3% of the province overall.8,9 The Thunder Bay Regional Health Sciences Centre (TBRHSC) is a 375-bed hospital that functions as the primary referral centre for most of the region.
Population-based monitoring of the epidemiologic impact of PSGN is lacking in Ontario because it is not currently a reportable disease. The aim of our study was to measure the incidence of PSGN and resulting complications in northwestern Ontario, including among Indigenous and rural populations.
METHODS
We conducted a cross-sectional study of all cases of PSGN managed at TBRHSC over an 8-year period, from January 1, 2010, to December 31, 2017. We first performed an electronic search of the health records database using the discharge diagnosis of unspecified nephritic syndrome (code N05.9 in the International Classification of Diseases10), and we subsequently reviewed patient charts to identify cases of PSGN and those requiring dialysis. This project was approved by the research ethics board of TBRHSC.
Similar to previous studies,6,11 we classified cases as confirmed, probable, or possible based on the type of evidence available (ie, definitive, clinical, laboratory, or expert opinion), as shown in Table 1. Evidence of preceding GAS infection included elevated antistreptolysin O titre or positive throat culture for GAS. Rurality was defined as primary residency in a community with a population of fewer than 10,000 people.12 Indigenous status was defined as having health insurance coverage provided by First Nations and Inuit Health.
PSGN diagnostic criteria definitions: A) Evidence type and B) case type.
We calculated incidence rates and incidence rate ratios of all, pediatric (<18 years), and adult PSGN cases, and of those requiring dialysis, using 2011 and 2016 census data to determine the overall and Indigenous population numbers for northwestern Ontario.13 We used linear interpolation and extrapolation to estimate the population in non-census years. The sum of the population over the 8 years was used to determine the total person-years for the incidence rate calculations. The rural population was estimated as 34.2% of the population and a gender distribution of 50.7% female was used.9,13 We used Fisher exact tests to determine the 95% CIs.14
RESULTS
Over the 8-year study period we observed 33 cases of PSGN (mean=4 cases; range 0 to 11 cases per year) translating to a mean annual incidence rate of 1.8 (95% CI 1.2 to 2.5) per 100,000 person-years (range 0.0 to 4.8 per 100,000 person-years). The mean age (SD) was 36 (24) years with 61% (n=20) male and 58% (n=19) Indigenous patients. The pediatric and adult mean annual incidence rates were 2.6 (95% CI 1.3 to 4.9) and 1.6 (95% CI 1.0 to 2.4) per 100,000 person-years, respectively. Among the 10 pediatric cases, the mean age was 9 years (range 3 to 17 years), with 70% (n=7) male and 70% (n=7) Indigenous patients. Among the 23 adult cases, the mean age was 49 years (range 25 to 80 years), with 57% (n=13) male and 57% (n=13) Indigenous patients.
Of the 33 cases, 28 were confirmed with renal biopsy or clinical and laboratory data (Table 2). Indigenous patients accounted for 61% (n=17) of the confirmed cases. The mean annual incidence rate of PSGN was 3.6 (95% CI 2.1 to 5.8) per 100,000 person-years for Indigenous patients, compared with 0.6 (95% CI 0.3 to 1.1) per 100,000 person-years for non-Indigenous patients (incidence rate ratio [IRR]=6.0; 95% CI 2.8 to 13, P<.001). The mean annual incidence rate of PSGN cases requiring dialysis was 2.1 (95% CI 1.0 to 3.9) per 100,000 person-years for Indigenous patients compared with 0.2 (95% CI 0.1 to 0.6) per 100,000 person-years for non-Indigenous patients (IRR=9.6; 95% CI 3.0 to 31, P<.001). Rural patients accounted for 71% (n=20) of the confirmed cases (IRR=3.2; 95% CI 1.4 to 7.3, P=.006). Compared with urban patients, the IRR for dialysis for rural patients was 3.9 (95% CI 1.0 to 10, P=.02).
Mean annual incidence rates and rate ratios of PSGN and PSGN requiring dialysis in northwestern Ontario, 2010 to 2017: A) All cases, B) pediatric cases, and C) adult cases.
The mean annual incidence rate of pediatric PSGN cases was 6.1 (95% CI 2.2 to 13) per 100,000 person-years for Indigenous patients compared with 0.5 (95% CI 0.1 to 1.9) per 100,000 person years for non-Indigenous patients (IRR=12; 95% CI 5.5 to 25, P<.001). No non-Indigenous pediatric patients required dialysis. Of the 23 adult cases, Indigenous patients accounted for 55% (n=11) of the confirmed cases. The mean annual incidence rate of adult PSGN cases was 2.9 (95% CI 1.5 to 5.3) per 100,000 person-years for Indigenous patients compared with 0.6 (95% CI 0.3 to 1.0) per 100,000 person-years for non-Indigenous patients (IRR=4.7; 95% CI 2.2 to 10, P<.001).
DISCUSSION
Indigenous and rural populations in northwestern Ontario are disproportionately affected by PSGN compared with their non-Indigenous and urban counterparts. The Indigenous population of northwestern Ontario represents 21.5% of the total population but accounted for 61% of the confirmed PSGN cases. Overall, Indigenous patients were 6 times as likely to develop PSGN and were nearly 10 times as likely to require dialysis compared with their non-Indigenous counterparts. Rates for both measures were also statistically significantly higher for Indigenous patients compared with non-Indigenous patients in subanalyses of both the pediatric and adult populations. The rural population of northwestern Ontario represents approximately 34.2% of the total population but composed 82% of the confirmed PSGN cases. Patients living in rural areas were more than 3 times as likely to have PSGN and nearly 4 times as likely to require dialysis compared with their urban counterparts. Both measures were statistically significantly higher for the rural population of adults compared with urban adults, but no differences were seen between rural and urban populations of pediatric patients.
A 2016 study in a subregion of northwestern Ontario had mean annual incidence rates of 20.8 per 100,000 person-years for the pediatric population and 4.0 per 100,000 person-years for the adult population.6 Our estimate is much lower, possibly owing to cases of patients from the region who were diagnosed outside of TBRHSC, thus leading to a substantial underestimation of the true incidence.6,7 Rather than reporting true incidence, our estimated annual incidence rate is meant to establish the minimum incidence of PSGN in northwestern Ontario, as population-based public health monitoring is lacking.
The finding of Indigenous and rural populations being disproportionately affected by PSGN compared with their non-Indigenous and urban counterparts is consistent with population-based studies in a subregion of northwestern Ontario and from the Northern Territory of Australia.6,7,15,16 It is well known that rural populations have an increased burden of PSGN compared with urban populations, which is thought to be owing mainly to the social determinants of health.1,3 However, barriers in accessing health care, including coordinated secondary prophylaxis programs, may be contributing factors of the high burden of PSGN seen in this region, which consists of many isolated communities, some of which have only intermittent health care access.17,18
Limitations
Our study has several limitations. Clinical data were retrospectively obtained from patient charts and some patient outcomes had not been recorded. Several patients who were identified as having PSGN lacked complete microbiological and clinical data and therefore were classified as having probable or possible PSGN. Furthermore, the identification of participants required accurate International Classification of Diseases discharge summary coding, and if it were inaccurate cases would be missed. Although it is the main referral site, TBRHSC is not the only referral hospital for the catchment of northwestern Ontario, with academic hospitals in Winnipeg, Man, and southern Ontario receiving patient transfers for various reasons, including weather, hospital capacity, patient preference, and acuity and severity of disease. In addition, our study evaluated only those patients admitted to TBRHSC, and therefore the severity of PSGN, including dialysis requirements, may not be representative of PSGN cases not requiring hospital admission. Given these limitations, the incidence of PSGN is likely substantially underestimated, but it is uncertain whether the extent of underestimation is similar for Indigenous and non-Indigenous populations or for rural and urban populations. In addition, Indigenous status was based on health insurance data, which excludes non-status Indigenous, Inuit, and Métis patients. Finally, owing to small numbers of cases, we were unable to control for confounding variables to determine the independent effects of Indigenous status and rural residence.
Conclusion
The main burden of PSGN in northwestern Ontario occurs among Indigenous and rural populations. Further research is required to investigate the true burden of PSGN in this area owing to limitations of this study. In collaboration with regional Indigenous groups, we advocate for PSGN being made a reportable disease. These findings should serve as an impetus for public health action.
Acknowledgments
The authors are grateful for the help and advice of Jenna Johns, Research Lead at Nishnawbe Aski Nation; Dr Marina Ulanova, Professor of Immunology at NOSM University in Thunder Bay, Ont; Sacha Dubois, Assistant Professor of Biostatistics and Research Methodology at NOSM University in Lakehead, Ont; and the Health Records Department at Thunder Bay Regional Health Sciences Centre. Funding for this project was received from the Senate Research Committee Research Development Fund at Lakehead University.
Notes
Editor’s key points
▸ Poststreptococcal glomerulonephritis (PSGN) is a disease linked with social inequality that has been identified as a public health concern in northwestern Ontario. However, information about the impact of PSGN is lacking because it is not currently a reportable disease.
▸ Indigenous people and rural populations have higher burdens of PSGN than their non-Indigenous and urban counterparts in the region. This includes being more likely to require dialysis as part of their treatment for PSGN, which suggests more severe disease.
▸ The incidence of PSGN in northwestern Ontario is likely higher than this initial study suggests. Additional work is needed to understand the burden of PSGN in the region and to address health disparities affecting Indigenous and rural populations.
Points de repère du rédacteur
▸ La glomérulonéphrite post-streptococcique (GNPS), est une maladie associée à l’iniquité sociale qui a été identifiée comme étant une préoccupation de santé publique dans la région au Nord-Ouest de l’Ontario. Par ailleurs, les renseignements au sujet des répercussions de la GNPS sont insuffisants, parce que cette maladie n’est actuellement pas à déclaration obligatoire.
▸ Les populations autochtones et rurales sont plus fortement touchées par la GNPS que leurs homologues non autochtones et urbaines de la région. Par exemple, il est plus probable qu’elles nécessitent une dialyse comme composante de leur traitement de la GNPS, ce qui laisse entendre une maladie plus sévère.
▸ L’incidence de la GNPS dans le Nord-Ouest ontarien est probablement plus élevée que le fait valoir cette étude initiale. D’autres travaux sont requis pour comprendre le fardeau de la GNPS dans la région et pour régler les disparités en santé qui affectent les populations autochtones et rurales.
Footnotes
Contributors
Dr Joelle Thorgrimson contributed to the study design, collected and statistically analyzed the data, and contributed to writing the manuscript. Dr Jeffrey C. Kwong contributed to statistical analysis of data and manuscript review. Dr Daniel Dalcin conceived of and designed the study, analyzed the data, and contributed to writing the manuscript. All authors read and approved the final manuscript.
Competing interests
None declared
This article has been peer reviewed.
Cet article a fait l’objet d’une révision par des pairs.
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