Abstract
Objectives
Increased numbers of pertussis cases in September 2015 led to the declaration of an outbreak in the Saskatoon Health Region (SHR). SHR (population approximately 350,000) is a geographic area in central Saskatchewan consisting of both urban and rural municipalities. The purpose of this study was to describe the epidemiology and identify possible predictors of the outbreak.
Methods
Confirmed cases of pertussis in SHR from 2010 to 2015 were extracted from the integrated Public Health Information System (iPHIS) database. Univariate and bivariate analyses and a comparison of the two outbreaks were conducted. Poisson regression modelling was used to estimate incidence rate ratios (IRRs) of factors associated with pertussis infection.
Outcomes
Two outbreaks between 2010 and 2015. Factors associated with the 2015 outbreak were residence in rural areas (IRR = 18.67, 95% CI 11.82–29.49; 11.37, 95% CI 6.40–20.21; and 6.31, 95% CI 3.43–11.62) for Humboldt, Watrous, and Rosthern areas, respectively, compared to the City of Saskatoon, and among children 11–14 years of age (IRR = 3.11, 95% CI 1.67–5.79) compared to children under 5 years of age. Unvaccinated persons had increased risk (IRR = 1.60, 95% CI 1.07–2.38). Multiple interventions, including enhanced contact tracing, supplemental immunization clinics, and cocooning, were employed in the 2015 outbreak.
Conclusion
Pertussis is a cyclical disease with outbreaks occurring every 3 to 5 years. Teenagers have increased risk of disease compared to younger children, likely due to waning immunity. Rural residents had a higher incidence of disease, possibly due to clusters of conscientious objectors. Control efforts require recognition of waning immunity and unvaccinated susceptibles.
Résumé
Objectifs
Une augmentation des cas de coqueluche en septembre 2015 a mené à la déclaration d’une flambée dans la Région sanitaire de Saskatoon (RSS). La RSS (environ 350,000 habitants) est une zone géographique du centre de la Saskatchewan qui englobe à la fois des municipalités urbaines et rurales. Nous avons voulu décrire l’épidémiologie de cette flambée et en cerner les prédicteurs possibles.
Méthode
Les cas confirmés de coqueluche survenus dans la RSS entre 2010 et 2015 ont été extraits de la base de données du Système intégré d’information sur la santé publique (SIISP). Des analyses univariées et bivariées et une comparaison de deux flambées ont été effectuées. Par modélisation de la régression de Poisson, nous avons estimé les rapports de taux d’incidence (RTI) des facteurs associés à l’infection par la coqueluche.
Résultats
Il y a eu deux flambées entre 2010 et 2015. Les facteurs associés à la flambée de 2015 étaient le fait de résider dans les régions rurales de Humboldt, Watrous et Rosthern, respectivement (RTI = 18,67, IC de 95 % 11,82–29,49; 11,37, IC de 95 % 6,40–20,21; et 6,31, IC de 95 % 3,43–11,62) comparativement à la Ville de Saskatoon et d’être un enfant de 11 à 14 ans (RTI = 3,11, IC de 95 % 1,67–5,79) comparativement à un enfant de moins de 5 ans. Le risque était plus élevé chez les personnes non vaccinées (RTI = 1,60, IC de 95 % 1,07–2,38). Plusieurs interventions, dont le retraçage renforcé des contacts, l’ajout de cliniques de vaccination et le cocooning, ont été employées durant la flambée de 2015.
Conclusion
La coqueluche est une maladie cyclique dont les flambées surviennent tous les trois à cinq ans. Les adolescents y sont plus vulnérables que les enfants plus jeunes, probablement en raison de la baisse de leur immunité. L’incidence de la maladie était plus élevée dans la population rurale, ce qui pourrait s’expliquer par la présence de grappes d’objecteurs de conscience. Pour lutter contre la coqueluche, il faut donc tenir compte de la baisse de l’immunité et des réceptifs non vaccinés.
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Notes
A case is defined based either on isolation of Bordetella pertussis from appropriate specimen or detection of B. pertussis DNA from appropriate specimen and the presence of one or more of the following:
-
i.
Cough lasting 2 or more weeks;
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ii.
Paroxysmal cough of any duration;
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iii.
Cough with inspiratory whoop or ending in vomit or gagging.
A case can also be identified if there is epidemiologic linkage to a laboratory-confirmed case with the presence of one of the following:
-
i.
Paroxysmal cough of any duration;
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ii.
Cough with inspiratory whoop or ending in vomit or gagging.
-
i.
These are geographic areas identified in Saskatoon Health Region and include City of Saskatoon, Saskatoon and area (i.e., bedroom communities of Saskatoon), Rosthern and area, Humboldt and area, and Watrous and area.
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Acknowledgements
We thank Rhonda Bryce, Chel Lee, Hyun Lim, and Keseina Akpoigbe for statistical support provided during the preparation of this manuscript.
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Appendix
Appendix
Epidemic curve of the pertussis outbreak in Saskatoon Health Region, 2015 (n = 114)
Graph showing timelines of public health response to 2015 pertussis outbreak in SHR
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Medu, O., Anderson, M., Enns, A. et al. Predictors of pertussis outbreak in urban and rural municipalities of Saskatchewan, Canada. Can J Public Health 109, 362–368 (2018). https://doi.org/10.17269/s41997-018-0074-1
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DOI: https://doi.org/10.17269/s41997-018-0074-1