Abstract
Background: The tuberculosis control strategy of vaccinating First Nations newborns with BCG (bacille Calmette-Guérin) is currently undergoing re-evaluation in Canada. Review of recent pediatric tuberculosis morbidity could inform this re-evaluation.
Methods: Potential source cases and pediatric cases of tuberculosis from Alberta First Nations were identified over the 10 years 1991–2000. The distribution of pediatric disease was described. The effect of BCG on tuberculosis morbidity in two large outbreaks was determined.
Results: A total of 57 potential source cases and 41 pediatric cases of tuberculosis were reported from 17 (41.5%) and 8 (19.5%) of the 41 on-reserve First Nation Community Health Centres, respectively. Three outbreaks traceable to three source cases accounted for 34 (18, 3, and 13, respectively) of the 41 (82.9%) pediatric cases. Each outbreak was spatially and temporally separate from the other. Each outbreak strain of Mycobacterium tuberculosis had a unique DNA fingerprint. In the largest outbreaks, disease-to-infection ratios (secondary case rates) were higher in newly infected unvaccinated versus vaccinated close pediatric contacts (12/13 [92.3%] versus 7/15 [46.7%], p=0.02), but the infection rate was almost certainly falsely high in the BCG vaccinated. One unvaccinated child had a brain tuberculoma in addition to primary pulmonary tuberculosis.
Conclusion: For most Alberta First Nations communities, the spatial and temporal distribution of disease, and the meager impact on morbidity, challenge the rationale for continued use of BCG.
Résumé
Contexte: On réévalue actuellement au Canada la stratégie de contrôle de la tuberculose qui consiste à vacciner les nouveau-nés des Premières nations par le BCG (bacille Calmette-Guérin). Un examen de la morbidité récente due à la tuberculose infantile pourrait étayer cette réévaluation.
Méthode: Nous avons relevé les cas sources potentiels et les cas de tuberculose infantile chez les Premières nations de l’Alberta pendant la décennie 1991–2000, puis décrit la répartition de la maladie infantile. Nous avons ensuite déterminé l’effet du BCG sur la morbidité due à la tuberculose lors de deux grandes poussées épidémiques.
Résultats: En tout, 57 cas sources potentiels ont été déclarés dans 17 des 41 centres de santé communautaire des Premières nations dans les réserves (41,5 %), et 41 cas de tuberculose infantile ont été déclarés dans 8 des 41 centres (19,5 %). Trois poussées épidémiques dont a pu retracer les trois cas sources ont été à l’origine de 34 (18, 3 et 13, respectivement) des 41 cas de tuberculose infantile (82,9 %). Chaque poussée était distincte des autres dans l’espace et dans le temps. Chaque souche épidémique de Mycobacterium tuberculosis avait sa propre empreinte génétique. Lors des plus grosses poussées, les rapports maladie/infection (les taux d’attaque secondaire) étaient plus élevés chez les enfants non vaccinés nouvellement infectés en contact étroit avec des personnes atteintes que chez les enfants vaccinés (12/13 [92,3 %] contre 7/15 [46,7 %], p=0,02), mais le taux d’infection était presque certainement faussement élevé chez les enfants vaccinés par le BCG. L’un des enfants non vaccinés présentait un tuberculome des méninges en plus d’une tuberculose pulmonaire primaire.
Conclusion: Dans la plupart des communautés des Premières nations de l’Alberta, la répartition de la maladie dans le temps et dans l’espace et le maigre effet du BCG sur la morbidité mettent en doute le bien-fondé de continuer à administrer le vaccin.
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