The incidence of giant cell arteritis in Ontario, Canada.

OBJECTIVE:The incidence of giant cell arteritis (GCA) is insufficiently documented for Canada, but important to ascertain for public health planning. We estimate the incidence of biopsy-proven GCA (BPGCA) in Kingston, Ontario, and for the province of Ontario. METHOD:The number of cases of BPGCA was tabulated from retrospective chart review of all temporal artery biopsies (TABx) in Kingston, Ontario from 2011-15. The relevant population denominator was determined from the Canada census federal electoral district and the patient's postal code. The province-wide estimate for the incidence of BPGCA was calculated from provincial billing data of TABx from 2015-17, the Canada census for Ontario, and the expected positive yield of TABx. RESULTS:There were 35 subjects with BPGCA in the Kingston area over the 4-year period, from a population of 179 503 individuals 50 years of age or older (≥50 years). Ontario billing data identified 2404 patients who underwent TABx for suspected GCA over a 2-year period, from a population of 5 143 610 persons ≥50 years. Meta-analysis of 5 provincial TABx series suggested a 21% positive yield from TABx procedures (95% CI 0.18-0.24). The minimum cumulative incidence of BPGCA was 4.9 per 100 000 persons ≥50 years in Kingston, and 4.9 (95% CI 4.2-5.6) per 100 000 persons ≥50 years for Ontario as a whole. CONCLUSION:The estimated incidence of BPGCA in Ontario using 2 different estimation techniques was comparable, but low compared with other countries. The actual incidence of GCA in Ontario may be higher.