National Lyme Disease Surveillance in Canada 2009–2012

Table of contents:

• Introduction
• A summary of Lyme disease cases
• Traveled-acquired Lyme disease cases
• Lyme disease cases by age and gender
• Seasonal variation in Lyme disease risk
• Where in Canada Lyme disease cases were acquired
• The symptoms of Lyme disease are being reported in Canada
• Interpretation and conclusions
• Acknowledgments
• References
• Technical notes

Introduction

Lyme disease became nationally notifiable in 2009 and surveillance data are provided by every province and territory through the National Notifiable Disease Surveillance System (NNDSS). Some provinces (Alberta, Manitoba, Ontario, New Brunswick, Nova Scotia and Prince Edward Island) participate in the Lyme disease enhanced surveillance (LDES) system, which aims to better identify Canadians at risk by analysis of information on reported human cases that is additional to information normally transferred to the NNDSS. Through collection of these data we aim to track the incidence of Lyme disease in Canada, and better understand how incidence is changing from year to year, where Lyme disease cases are occurring in Canada, age and gender groups most at risk, and what clinical manifestations are being seen in Canada. Collection and analysis of National Lyme disease surveillance data provides information that has two aims: i) supporting prevention of Lyme disease by helping to target control and prevention activities to the population most at risk; and ii) supporting improved diagnosis and treatment of affected Canadians by informing health care workers of the clinical manifestations of Lyme disease most frequently reported in Canada. Together these objectives aim to minimise the impact of Lyme disease in Canada.

A summary of Lyme disease cases

In 2012, 338 probable and confirmed cases were reported by 8 provinces (British Columbia, Alberta, Manitoba, Ontario, Quebec, New-Brunswick, Nova Scotia and Prince Edward Island: Figure 1). The number of cases reported in Canada has more than doubled in four years, from 144 in 2009 to 338 in 2012 (Table 1, Figure 2: but see the technical notes regarding these data), which is an increase in incidence from 0.4 to 1.0 cases per 100,000 population. Increasing incidence was mostly due to an increase in the number of cases that were most likely acquired in Canada, which comprised 65% of cases in 2009 and 82% of cases in 2012 (Figure 2). For all cases from 2009-2012, 62.2% of domestically-acquired cases were reported as confirmed (i.e. were mostly disseminated Lyme disease with serological laboratory evidence of infection and were acquired in a known endemic area) and 37.8% were reported as probable according to the surveillance case definition (i.e. were early Lyme disease acquired in a known endemic area or were disseminated Lyme disease with laboratory evidence of infection, but no contact with a known endemic area: Public Health Agency of Canada, 2009).

Figure 1. The numbers of reported Lyme disease cases by province in Canada in 2012.

Figure 2. The numbers of reported Lyme disease cases in Canada 2009-2012.

Travel-acquired Lyme disease cases

For the period 2009-2012, data on country of exposure was available for 80.5% of cases from provinces participating in the LDES. A total of 48 cases (22.1% of those for which information was available) were reported as having been acquired outside Canada in 2012. Since 2009, the annual number of cases acquired during travel outside Canada has remained similar (41, 38 and 41 respectively for 2009, 2010 and 2011).  All cases from Alberta were acquired while travelling outside Canada. For the 54 cases for which the location of travel outside Canada was provided during the period 2009-2012, 70% were acquired in the USA and 30% were-acquired in Europe.

Lyme disease cases by age and gender

There were more men than women affected (56% vs 44%). Incidence of reported cases was highest for adults aged between 55 and 74, and amongst children incidence was highest for those aged between 5 and 14 (Figure 3).

Figure 3. The incidence of reported Lyme disease cases by sex and age category 2009-2012.

Data were available from all cases from all provinces. The denominators for these age and sex categories were obtained from Statistics Canada.

Seasonal variation in Lyme disease risk

Data on date of onset or diagnosis of illness were reported from the provinces participating in the LDES. Most domestically-acquired cases (95%) were reported from April through November peaking in July when tick vectors are active and when Canadians are frequently involved in outdoor activities (Figure 4). Reporting of some Lyme disease cases in each month from December to March could suggest that there may be risk outside the usual season of tick activity and that ticks can become active during warm periods during the winter in some locations, although this observation could be due to delayed onset of clinical manifestations in some instances (Wormser et al. 2006).

Figure 4. The numbers of Lyme disease cases reported in the LDES, by month of illness onset and by year, 2009-2012.

Where in Canada Lyme disease cases were acquired

For the 414 (46.5%) cases for which information on location of acquisition in Canada was available, nearly 90% were acquired in locations in the Maritimes, southern, eastern and north-western Ontario, and southern Manitoba where surveillance shows that the tick vectors of Lyme disease are known to occur (Ogden et al. 2014; Figure 5).

The identification of cases that are reported to have been acquired in areas where tick populations have not yet been identified will help inform future field surveillance for ticks.

Figure 5. The numbers of reported Lyme disease cases by municipality of acquisition, 2009-2012.

The symptoms of Lyme disease being reported in Canada

Over the period 2009-2012, a high proportion of cases (70%) were reported to have had symptoms of early Lyme disease (i.e. they showed erythema migrans [EM]). However, 55% of cases reported symptoms of disseminated Lyme disease: 28% of cases reported symptoms of early disseminated Lyme disease (i.e. neurological and cardiac symptoms) and 38% of cases reported symptoms of late Lyme disease (i.e. arthritis) (Figure 6). Of those cases acquired in known Canadian Lyme disease endemic or Lyme risk areas (defined in Ogden et al. 2014) 40% were reported as early Lyme disease, i.e. EM was the only reported symptom. For 37% of cases acquired in Canada for which EM was reported, clinical manifestations of later stages of Lyme disease were also reported.

Figure 6. The clinical manifestations of Lyme disease cases for which these data were reported, 2009-2012.

Interpretation and conclusions

Endemic lyme disease occurs in British Columbia and in the eastern and central Canadian provinces of Nova Scotia, New Brunswick, Quebec, Ontario and Manitoba where it is continuing to emerge (Figure 1 and 2, Table 1). Lyme disease cases that were acquired while travelling in the USA or Europe continue to be reported in a number of provinces at a fairly constant rate since surveillance began (Table 2). Males, children aged between 5 and 14 years and adults between 50 and 74 years may be particularly at risk (Figure 3). Lyme disease cases are reported in all months but peak incidence occurs in the summer months (Figure 4). Most Lyme disease cases were reported as having been acquired in areas where Lyme disease risk associated with tick populations is known (Figure 5). Some cases reported acquisition in areas where established tick populations and Lyme disease risk has not been identified to date (Figure 5). These sporadic case reports may occur as a result of exposure to infected ticks dispersed by migratory birds (Ogden et al. 2008), or they may be the early indications of newly establishing tick populations in locations where field surveillance for ticks has yet to be conducted (Ogden et al. 2014). EM was reported in a high proportion of cases (Figure 6), but Lyme disease was diagnosed and/or reported at this early stage of infection (when EM is the only symptom) in a low proportion of cases (40%) compared to the proportion of cases reported as early Lyme disease in surveillance in the USA (> 60%: Bacon et al. 2008), where awareness of Lyme disease amongst the public and medical practitioners would be expected to be greater than in Canada. Therefore, affected members of the public in Canada are not presenting themselves for treatment in early Lyme disease, and/or front line medical practitioners are not reporting all early Lyme disease cases. This could be attributable to suboptimal awareness amongst health care workers and the public.

Early identification, diagnosis and treatment are key to successful health outcomes for Canadians suffering from Lyme disease. The above findings, combined with the growing proportion of cases acquired within Canada, support the need for a coordinated response to Lyme disease in Canada. As such, the Public Health Agency of Canada implemented an Action Plan on Lyme disease (Harymann et al. 2014), with the objective of increasing awareness among physicians and Canadians, enhancing surveillance and improving diagnosis.

Acknowledgments

The PHAC would like to thank all our partners at provincial and regional levels across Canada who contribute to the data collection and transfer and made this report possible.

References

• Bacon RM, Kugeler KJ, and Mead P (2008). Surveillance for Lyme Disease United States, 1992-2006. Morbidity and Mortality Weekly Report, 57.
• Harymann M, Ogden N, Lindsay R, Lawless V, Deilgat M, and Sternthal S (2014). Summary of the Public Health Agency of Canada's Action Plan on Lyme disease. Can Commun.Dis. Rep., 40, 88-90.
• Ogden NH, Koffi JK, Pelcat Y, and Lindsay LR (2014). Environmental risk from Lyme disease in central and eastern Canada: a summary of recent surveillance information. Can.Commun.Dis.Rep., 40, 74-82.
• Ogden NH, Lindsay LR, Hanincova K et al. (2008). Role of migratory birds in introduction and range expansion of Ixodes scapularis ticks, and Borrelia burgdorferi and Anaplasma phagocytophilum in Canada. Appl.Environ.Microbiol., 74, 1780-1790.
• Public Health Agency of Canada (2009). Cases definitions for diseases under national surveillance. Can.Commun.Dis.Rep.,  35.
• Wormser GP, Dattwyler RJ, Shapiro ED et al. (2006). The clinical assessment, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin. Infect. Dis., 43, 1089-1134.

Technical notes

1. The data analyzed and presented in this report are provided by provincial public health authorities. The data represent cases reported to public health units and recorded in the different provincial notifiable diseases systems. Counts by province are subject to varying degrees of underreporting.
2. Many provincial notifiable diseases systems are dynamic disease reporting systems that permit ongoing updates to the data if new information on cases comes to light. Therefore, data extracted from a provincial notifiable disease system represent a snap shot at the time of extraction and may differ from previous or subsequent reports.
3. For this reason, data in this report may differ slightly from data displayed by provincial authorities.
4. Data on possible area of exposure, travel and symptoms are provided by provinces that participate in the LDES.