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Can local risk of West Nile virus infection be predicted from previous cases? A descriptive study in Quebec, 2011–2016



This study aimed at (1) describing the local risk of West Nile virus (WNV) infection in humans based on previous case reports and (2) investigating the spatial clustering of cases in the five most affected administrative regions of Quebec, Canada, for the 2011–2016 period.


Human WNV cases declared to the Ministry of Health and Social Services of Quebec (Ministère de la santé et des services sociaux, MSSS) were retrieved. Incidence risk by age and sex was calculated for the study period. The yearly and monthly occurrence of cases in geographical units (GUs) was described and the probability of observing cases in a GU with cases reported in the previous year or month was assessed. Moran’s I was used to assess global clustering across the study area. Spatial clusters were identified by the Kulldorff scan statistic.


A total of 261 WNV cases were declared to the MSSS between 2011 and 2016 in the study area. Overall, a low percentage of GU with cases reported had additional cases reported over the next month or year. Global spatial clustering was weak but statistically significant (p < 0.05) for 2012 and 2015. For these two years, spatial clusters of high-risk GUs were identified.


Results underline the challenge of predicting the distribution of WNV incidence risk in Quebec based on previous occurrence of human cases. Ongoing research with high spatial resolution entomological data is still necessary to understand the spatial distribution of risk at a local scale.



Cette étude visait à (1) décrire le risque local d’infection par le virus du Nil occidental (VNO) chez l’humain à partir des cas rapportés de 2011 à 2016 et (2) estimer le degré d’organisation spatiale de ces cas dans les cinq régions administratives du Québec les plus affectées par le VNO au cours de cette période.


Le risque d’incidence de VNO chez l’humain a été calculé, selon l’âge et le sexe des patients, à partir de la liste des cas déclarés au Ministère de la santé et des services sociaux du Québec (MSSS) au cours de la période à l’étude. La distribution annuelle et mensuelle des cas à travers les unités géographiques (UG) à l’étude a été décrite. La probabilité d’observer des nouveaux cas dans une unité géographique où des cas avaient déjà été rapportés au cours de l’année ou du mois précédent a été calculée. Le degré d’agrégation spatiale a été évalué à l’aide du I de Moran. Les agrégats spatiaux ont été identifiés à l’aide du scan de Kulldorff.


Au total, 261 cas de VNO ont été déclarés au MSSS entre 2011 et 2016 dans la zone d’étude. Un faible pourcentage d’UG ayant eu des cas rapportés à une période donnée ont eu des nouveaux cas au cours du mois suivant ou de l’année suivante. Le degré d’agrégation spatiale des cas était faible dans la zone d’étude mais statistiquement significatif (p < 0,05) pour 2012 et 2015. Pour ces deux années, des agrégats spatiaux de cas ont été identifiés.


Il est difficile de prédire la distribution du risque d’incidence du VNO au Québec en se basant sur les cas humains rapportés dans le passé. Des données entomologiques ayant une haute définition spatiale sont requises afin de comprendre la distribution spatiale du risque de VNO à une échelle locale.

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The authors wish to thank the Directions régionales de la santé publique of Lanaudière, Laurentides, Laval, Montréal and Montérégie for their collaboration in the data collection process, Marie-Josée Archetto for coordinating the data collection, and collaborators from the SIDVS-VNO for their help with the epidemiological database.

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Correspondence to Jean-Philippe Rocheleau.

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All procedures performed in this study were in accordance with the ethical standards of the Comité d’éthique de la recherche en santé de l’Université de Montréal (protocol 14-135-CERES-D) and with the 1964 Helsinki declaration and its later amendments.

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Rocheleau, J., Kotchi, S. & Arsenault, J. Can local risk of West Nile virus infection be predicted from previous cases? A descriptive study in Quebec, 2011–2016. Can J Public Health (2020). https://doi.org/10.17269/s41997-019-00279-0

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  • West Nile virus
  • Risk distribution
  • Human
  • Spatiotemporal
  • Public health


  • Virus du Nil occidental
  • Distribution du risque
  • Humain
  • Spatiotemporel
  • Santé publique