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ObjectiveThis study aims to describe incidence over time, geographic and seasonal distribution, demographic and clinical characteristics of Lyme disease cases in Canada.IntroductionLyme disease (LD), a multisystem infection that is manifested by progressive stages (1), is emerging in central and eastern provinces of Canada due to northward expansion of the geographic range of Ixodes scapularis, the main vector in these regions (2). In 2004, approximately 40 human cases of LD were reported in Canada. In 2009, LD disease became nationally notifiable, with provincial and territorial health departments reporting clinician-diagnosed cases to the Public Health Agency of Canada (PHAC). This study summarizes seven years (2009-2015) of national surveillance data for LD in Canada.MethodsNational Lyme disease surveillance data is collected through two surveillance systems, the Canadian National Disease Surveillance System (CNDSS) and the Lyme disease enhanced surveillance system (LDES). The CNDSS collects only demographic data (age and sex), and information on episode date and case classification. The LDES system captures additional data, including: possible geographic location of infection (for both locally acquired and travel-related cases); clinical manifestations; and results of laboratory testing. Nine provinces out of ten participate to LDES that means they provide a part of or all the data elements of this surveillance system. The 2009 national Lyme disease case definition (3) that distinguishes confirmed and probable cases (Table 1) is used to classify and report cases diagnosed by clinicians.This study describes the incidence over time, seasonal and geographic distribution, demographic and clinical characteristics of reported LD cases. Logistic regression was used to explore variations among age groups, sex and year of reporting clinical manifestations to better understand potential demographic risk factors for the occurrence of LD. Different models were used with as outcomes absence or presence of: erythema migrans (early Lyme disease), neurologic and cardiac symptoms and multiple erythema, migrans (early disseminated Lyme disease); and arthritis (late disseminated Lyme disease). The most parsimonious multivariate models were sought by backward elimination of nonsignificant variables until all factors in the model were significant (P