Surveillance for Lyme disease in Canada, 2009-2019

Abstract

Background: Lyme disease (LD) is a multisystem infection that can affect the skin, heart, joints and nervous system. In Canada, the incidence of LD cases has increased over the past decade making this a disease of public health concern. The objective of this study is to summarize the epidemiology of LD cases reported in Canada from 2009 through 2019.

Methods: Incidence over time, case classification (confirmed and probable), seasonal and geographic distribution, demographic and clinical characteristics of reported LD cases were determined. Logistic regression was used to explore potential demographic risk factors for the occurrence of LD.

Results: During 2009-2019, a total of 10,150 LD cases were reported by the provinces to the Public Health Agency of Canada, of which 7,242 (71.3%) were confirmed and 2,908 (28.7%) were probable cases. The annual count increased from 144 in 2009 to 2,634 in 2019, mainly due to an increase in locally acquired infections, from 65.3% to 93.6%, respectively. The majority of cases (92.1%) were reported from three provinces: Ontario (46.0%); Nova Scotia (28.0%); and Québec (18.1%). Most of the locally acquired cases (74.0%) were reported in the summer months of June (20.0%), July (35.4%) and August (18.6%). The highest incidence rates (cases per 100,000 population) were in children aged 5-9 years (45.0) and in adults aged 65-69 years (74.3), with 57.3% of all reported cases occurring among males. The most common presenting symptoms were single erythema migrans rash (75.1%) and arthritis (34.1%). The frequency of reported clinical manifestations varied among age groups and seasons with erythema migrans and arthritis at presentation reported more frequently in children than older patients.

Conclusion: The results of this report highlight the continued emergence of LD in Canada and the need for further development and implementation of targeted awareness campaigns designed to minimize the burden of LD.

Keywords: Canada; Ixodes pacificus; Ixodes scapularis; Lyme disease; surveillance; tick-borne disease.

Figure 1

Number and proportion of Lyme disease cases, all reported and locally acquired (percentage^a) in Canada, 2009−2019 a Percentage of locally acquired cases among those cases with known location of probable acquisition in Canada

Figure 2

Month of illness onseta of Lyme disease cases acquired in Canada, 2009−2019 a Month of illness onset is the month of first symptoms seen

Figure 3

Reported locations of Lyme disease acquisitiona, Canada, 2009–2019 ^a Each dot on the map represents the probable location of infection acquisition, randomly distributed at the census subdivision level for all provinces except: Québec (2016–2018) and Nova Scotia (2019) used the administrative region and forward sortation area (FSA) of residency, respectively. In 2018, all of Nova Scotia was declared at risk of Lyme disease, and since then, the probable location of acquisition was based on the FSA of residency for cases with no travel history outside the province. Data on location of acquisition was not available at sub-provincial level for British Columbia and Saskatchewan; Saskatchewan reported one locally acquired case in 2017. Cases reported by Alberta and Newfoundland & Labrador were travel-related only. Hatched areas indicate Lyme disease risk areas. These are locations where surveillance activities suggest that populations of the Lyme disease vector, Ixodes scapularis have been established and the likely transmission of B. burgdorferi is occurring

Figure 4

Cumulative incidencea per 100,000 population of Lyme disease cases by age group and sex, Canada, 2009–2019 (n=7,667) a The denominators used to calculate the incidences were obtained from Statistics Canada, population estimates on July 1^st

Figure A1

Percentage of clinical manifestations by age group for locally acquired Lyme disease cases, in Canada, 2009−2019 (n=4,951)