Background/Purpose: Lupus incidence rates are known to differ by ethnicity among children and adults, with African ancestry as a risk factor for incident lupus, compared to those of European ancestry. Changes in a city’s ethnic demographic over time make it challenging to determine if changes in lupus incidence rates over time reflect population ethnic groups changes. We aimed to investigate whether lupus incidence rates have increased over time and whether trends over time differed by ethnic groups in Toronto, Canada—a large, multiethnic metropolitan area served by a tertiary care, pediatric lupus clinic.

Methods: Demographic information, including sex, self-identified ethnicity, age at diagnosis and region of residence, were prospectively collected on all children aged <18 years who were diagnosed with lupus between 1994 and 2015 in the pediatric lupus clinic at the Hospital for Sick Children (SickKids), Toronto. Only children living in Toronto were included in this analysis; those travelling to SickKids from outside of Toronto were excluded. Overall lupus incidence rates and 95% confidence intervals (95%CI) were calculated using population denominators for Toronto that were obtained from the Census of Canada, which is conducted every 5 years. Rates by age, sex and ethnicity were also calculated. Poisson models were used to calculate incidence rate ratios (IRR) and 95%CI for the year of diagnosis, to investigate whether rates of lupus incidence changed over the study period. Interaction terms between the year and ethnicity were tested to determine whether time trends in the rates of incident lupus differed by ethnicity.

Results: From 1994 to 2015, 503 children living in Toronto were diagnosed with lupus at SickKids, corresponding to an overall lupus incidence rate of 1.92 per 100,000 person-years (95%CI 1.75–2.09). Overall lupus incidence rates were highest among Chinese (3.77, 95%CI 2.96–4.58) and Black (3.62, 95%CI 2.88–4.35) children and lowest among White children (0.74, 95%CI 0.59–0.88). After adjusting for sex and age at diagnosis, the lupus incidence rate was found to increase by 5% each year from 1994 to 2015 (IRR 1.05, 95%CI 1.03–1.06). Interaction terms between the year and ethnicity were not statistically significant.

Conclusion: Pediatric lupus incidence increased over time in Toronto. While lupus incidence rates were substantially higher among Black and Chinese children, compared to White children, trends in the increase of lupus incidence did not differ over time between ethnic groups, but may reflect the changing ethnic population in Toronto.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/investigating-time-trends-in-incident-pediatric-lupus-across-ethnic-groups-in-toronto-canada-a-large-multiethnic-metropolitan-area/