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. 2019 Jan 3;44(1):32-37.
doi: 10.14745/ccdr.v45i01a04.

West Nile virus illness in Ontario, Canada: 2017

S Wijayasri  1 , M P Nelder  1 , C B Russell  1 , K O Johnson  1 , S Johnson  2 , T Badiani  1 , D Sider  1   3
Affiliations

West Nile virus illness in Ontario, Canada: 2017

S Wijayasri et al. Can Commun Dis Rep. .

Abstract

Background: In Canada, the annual incidence rates of West Nile virus (WNV) illness have fluctuated over the last 15 years. Ontario is one of the provinces in Canada most affected by WNV and, as a result, has implemented robust mosquito and human surveillance programs.

Objective: To summarize and discuss the epidemiology of WNV illness in Ontario, Canada in 2017, with comparisons to previous years.

Methods: Case data were obtained from the provincial integrated Public Health Information System. Provincial and public health unit (PHU)-specific incidence rates by year were calculated using population data extracted from intelliHEALTH Ontario.

Results: In 2017, the incidence of WNV illness in Ontario was 1.1 cases per 100,000 population, with 158 confirmed and probable cases reported by 27 of the province's 36 PHUs. This is the highest rate since 2013, but less than the rate in 2012 (2.0 cases per 100,000 population). Incidence rates in 2017 were highest in Windsor-Essex County and in PHUs in eastern Ontario. While the seasonality is consistent with previous years, the number of cases reported between July and September 2017 was above expected. Most cases were in older age groups (median: 58 years old) and males (59.5% of provincial total); cases with severe outcomes (neurological complications, hospitalizations, deaths) were also disproportionately in older males.

Conclusion: WNV illness continues to be an ongoing burden in Ontario. The increase in the number of cases reported in 2017, and the increased number of PHUs reporting cases, suggests changing and expanding risk levels in Ontario. Continued mosquito and human surveillance, increased awareness of preventive measures, and early recognition and treatment are needed to mitigate the impact of WNV infections.

Keywords: Culex; West Nile virus; climate; epidemiology; mosquito; public health; surveillance.

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Conflict of interest statement

Conflict of interest: None.

Figures

Figure 1
Figure 1. Number of confirmed and probable West Nile virus illness cases and incidence (per 100,000 population), by year, in Ontario, Canada, 2005–2017
Figure 2
Figure 2. Incidence of West Nile virus illness (per 100,000 population) in 2017, by public health unita, Ontario, Canada
Abbreviations: n, number; WNV, West Nile virus a Public health unit refers to the individual’s health unit of residence at the time of illness onset and not necessarily the location of exposure. Location of disease acquisition cannot be attributed to public health unit
Figure 3
Figure 3. Number of confirmed and probable West Nile virus illness cases reported in 2017, compared to four-year historical averages (2013–2016), by episode month, Ontario, Canada
Figure 4
Figure 4. Number of confirmed and probable West Nile virus illness cases reported in 2017 compared to four-year historical averages (2013–2016), by age groupa and sex, Ontario, Canada
a Age group refers to the age group (in years) of the individual at the time of illness
See this image and copyright information in PMC

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