Ticks and Lyme Disease Memo

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February 22, 2019

Introduction

The following analysis represents a summary of confirmed Lyme disease cases obtained from the iPHIS database for the 2018 calendar year inclusive for residents of Leeds, Grenville and Lanark. Where indicated, comparisons with other years have been provided.

Between 2010 and 2018 there have been 582 confirmed and probable cases of Lyme disease in Leeds, Grenville and Lanark according to data retrieved from iPHIS. Case counts decreased between 2017 and 2018 but still suggested a continuing upwards linear trend from 2010 (Figure 1). The median age of cases for 2018 was 57-years and about 62% were male.

Yearly Count of Lyme Disease Diagnosis — Figure 1: Year-over-year count of confirmed and probable Lyme cases in Leeds, Grenville and Lanark (2010-2018).

Assessment of Lyme Case Distribution for 2018

The majority of Lyme cases were reported in June of 2018 (Figure 2). In terms of municipality of Lyme case residence, the majority of cases were residing in the municipalities of Tay Valley, Leeds and the Thousand Islands and Rideau Lakes. However, about 19% of cases did not have a usable address linked to them (Figure 3).

Figure 2 Monthly Count — Figure 2: Lyme case distribution by month for 2018.

Figure 3 Municipality — Figure 3: Municipality of Lyme case residence (2018).

Assessment of the Geographic Distribution of Lyme Cases

It should be noted that the in following locational analysis of Lyme disease cases in Leeds, Grenville and Lanark from 2018, a full 21% (n = 20) of the 97 case were excluded as there were missing addresses or errors that did not allow for case locations to be geocoded. Therefore, the following spatial analyses represent an under-reporting of the actual Lyme disease case distribution in Leeds, Grenville and Lanark. As well, this analysis only represents the residence of the Lyme disease case and not the actual location where the tick vector was potentially acquired; making it a proxy estimate only.

The distribution of Lyme cases continues to increase in geographic extent across Leeds, Grenville and Lanark (Figure 4). The trend towards a more north and eastwards distribution of cases continues from what has been observed since 2010 (Figure 4).

Figure 4 Distribution — Figure 4: Distribution of geocoded Lyme cases (2018).

Assessment of the Syndromic Surveillance Tick-Related ED Visits

There were a total of 325 tick-related ED visits recorded for residents of Leeds, Grenville and Lanark in 2018 compared to 599 in 2017 and 425 in 2016. The distribution pattern for tick-related ED in 2018 was similar to that in 2016. However, there were fewer ED visits in the autumn months in 2018 and the frequency of visits occurred over a narrower time frame (mostly in October) (Figure 5, Table 1).

Figure 5 Hospital Visits — Figure 5: Hospital ED visits related to ticks for Leeds, Grenville and Lanark (2016-2018).

Table 1 Hospital Count — Table 1: Count of hospital ED visits related to ticks for Leeds, Grenville and Lanark (2016-2018).

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