Perspective: Incidence of Clinician-Diagnosed Lyme Disease in Manitoba, Canada 2009-2018.

Lyme disease (LD) surveillance yields useful information to monitor the disease trends and spatial distribution. However, due to several factors, the Manitoba Health surveillance system, as with other systems, could be subject to underreporting. To estimate the number and incidence of clinician-diagnosed LD over the study period in Manitoba, describe the epidemiology of clinician-diagnosed LD, and compare the findings with Manitoba Health LD surveillance data during the same period to estimate the extent of underreporting. A retrospective analysis of administrative health data was performed to calculate the number and incidence of clinician-diagnosed LD from 2009 to 2018 in Manitoba and describe the epidemiological characteristics using the , (ICD-10-CA and ICD-9-CM) codes, and antimicrobial drug prescriptions. Of the 1,629,698 registrants within the Manitoba Health Insurance Registry followed over 10 years, 1658 LD events were identified. Most of the cases occurred from May to July and corresponded to the peak activity of the nymphal stage of the blacklegged tick in the province. LD events presented a bimodal distribution with a peak in children between 5 and 9 years of age for both sexes, and a peak in adults from 65 to 84 and from 50 to 74, respectively, for males and females. We estimated that an average of 165 LD events occurred annually in Manitoba (mean annual incidence of 10.17 per 100,000 population), compared with 30 cases per year reported in the surveillance system; therefore, the LD surveillance yields an important underreporting.