Epidemiology and clinical manifestations of reported Lyme disease cases: Data from the Canadian Lyme disease enhanced surveillance system

Abstract

Lyme disease cases reported in seven Canadian provinces from 2009 to 2019 through the Lyme Disease Enhanced Surveillance System are described herein by demographic, geography, time and season. The proportion of males was greater than females. Bimodal peaks in incidence were observed in children and older adults (≥60 years of age) for all clinical signs except cardiac manifestations, which were more evenly distributed across age groups. Proportions of disease stages varied between provinces: Atlantic provinces reported mainly early Lyme disease, while Ontario reported equal proportions of early and late-stage Lyme disease. Early Lyme disease cases were mainly reported between May through November, whereas late Lyme disease were reported in December through April. Increased awareness over time may have contributed to a decrease in the proportion of cases reporting late disseminated Lyme disease. These analyses help better describe clinical features of reported Lyme disease cases in Canada.

Fig 1. Comparison of age and sex distribution between national surveillance and the LDES system, 2009–2019.

All Lyme disease cases in Canada (n = 9,969) and in the LDES subset (n = 4,690) with available data on age and sex were included. Incidence is per 100,000. The denominator in the LDES subset was the 7 provinces participating in the LDES with symptom data available for this study.

Fig 2. Incidence per 100 000 population of clinical manifestations reported for Lyme disease cases, Canada, 2009–2019.

Symptoms reported for single erythema migrans (EM) (n = 3,583), multiple EM (n = 309), Bell’s palsy (n = 320), other neurological symptoms (n = 858), Lyme carditis (n = 156), Lyme arthritis (n = 1,510). Age was missing for cases reporting single EM (n = 5) and Lyme arthritis (n = 1).

Fig 3. Geographic distribution of Lyme disease cases and proportion of cases by disease stage, Canada, 2009–2019*.

* Each dot represents the probable location of acquisition randomly distributed at the census subdivision level (n = 4,036) or the forward sortation area of residency for cases from Nova Scotia in 2019 (n = 373). The entire province of Nova Scotia was declared a LD risk area in 2018, so residency was inferred as the probable location of acquisition in the absence of travel history. Disease stage was available for 4,419 cases. The data on clinical manifestations are provided by provinces that are participating in the LDES and included in this analysis (British Columbia, Alberta, Ontario, New Brunswick, Nova Scotia, Newfoundland & Labrador [NL] and Prince Edward Island [PEI]). Manitoba participates in the LDES but was excluded from this analysis. Saskatchewan, Quebec and the Territories do not submit data to the LDES; instead, they provide limited information through the CNDSS. All cases reported by Alberta and Prince Edward Island were travel-related cases and thus not included on the map. All cases reported by British Columbia were either travel-related cases or had no location of acquisition at the sub-provincial level. No cases from Newfoundland & Labrador met inclusion criteria for the study.

Fig 4. Proportions of Lyme disease cases by month and by disease stage, Canada, 2009–2019.

Early localized cases (n = 2,339) were characterized as those presenting with only single erythema migrans (EM). Early disseminated cases (n = 851) were characterized as those reporting at least one of the following signs, with or without single EM: multiple EM, Bell’s palsy, other neurological signs, or cardiac signs. Late disseminated cases (n = 1,511) were characterized as any case reporting arthritis, with or without reporting any other sign or symptom. Error bars represent standard deviation.