Abstract
Background
On April 1, 2004, BCG (bacille Calmette-Guérin), a tuberculosis (TB) control vaccine, was discontinued in all but four high-risk communities in Alberta. To confirm the safety of vaccine withdrawal, and for future planning, the annual risk of infection (ARI) was determined in preschool First Nations children.
Methods
First Nations children born into reserve communities in Alberta between April 1, 1998 and March 31, 2004, and still living on reserve in 2004–2005, were identified. Health centre TB histories were validated by cross-referencing the birth cohort with the provincial TB Registry. Children that were not BCG vaccinated and not known to be tuberculin skin test (TST) positive underwent a TST. Birth cohort children were grouped as follows: (i) BCG vaccinated; (ii) BCG non-vaccinated, no TST; (iii) BCG non-vaccinated, TST; (iv) BCG vaccination status unknown. The ARI was calculated and the age and community characteristics of the groups were compared.
Results
There were 8,447 children in the 6-year birth cohort, 4,699 (55.6%) vaccinated, 2,696 (31.9%) non-vaccinated, and 1,052 (12.5%) whose vaccination status was unknown. Of the non-vaccinated children, 1,921 (71.3%) were tested and only 2 were TST positive. No other TST positive, BCG non-vaccinated children were identified in the TB Registry cross-match. The prevalence of infection in 2004–2005 was 0.1% and the ARI was 0.03%. The community risk of TB exposure was comparable in tuberculin-tested and non-tested BCG non-vaccinated children.
Conclusion
In low BCG-uptake First Nations communities in Alberta, the ARI is low and it is safe to withdraw BCG.
MeSH terms: BCG vaccine, mycobacterium infections
Résumé
Contexte
Le 1er avril 2004, le vaccin BCG (bacille Calmette-Guérin) contre la tuberculose a été abandonné partout en Alberta sauf dans quatre communautés à risque élevé. Afin de confirmer que le retrait du vaccin ne posait aucun danger et de planifier les programmes futurs, nous avons calculé le risque annuel d’infection (RAI) chez les enfants d’âge préscolaire membres des Premières nations.
Méthode
Nous avons répertorié les enfants membres des Premières nations nés dans les réserves de l’Alberta entre le 1er avril 1998 et le 31 mars 2004 qui vivaient toujours dans des réserves en 2004–2005. Nous avons ensuite validé les dossiers sur la tuberculose des centres sanitaires en faisant des recoupements entre la cohorte de naissance et le registre provincial sur la tuberculose. Les enfants n’ayant pas reçu le BCG et n’ayant pas eu un résultat positif à un test de sensibilité cutané à la tuberculine (TST) ont été soumis à un TST. Les enfants de la cohorte de naissance ont été regroupés comme suit: i) vaccinés par le BCG; ii) non vaccinés par le BCG, sans TST; iii) non vaccinés par le BCG, avec TST; iv) statut vaccinal inconnu par rapport au BCG. Nous avons calculé le RAI, puis comparé l’âge et les caractéristiques communautaires des groupes.
Résultats
Sur les 8 447 enfants dans la cohorte de naissance de six ans, 4 699 (55,6 %) étaient vaccinés, et 2 696 (31,9 %) ne l’étaient pas; le statut vaccinal des autres (1 052, soit 12,5 %) était inconnu. Sur les enfants non vaccinés, 1 921 (71,3 %) avaient été testés, et 2 seulement étaient positifs pour le TST. Aucun autre enfant positif pour le TST et non vacciné par le BCG n’a été identifié par recoupement avec le registre de la tuberculose. La prévalence de l’infection en 2004–2005 était de 0,1 %, et le RAI était de 0,03 %. Le risque communautaire d’exposition à la tuberculose était comparable chez les enfants non vaccinés par le BCG, qu’ils aient subi ou non le test cutané à la tuberculine.
Conclusion
Dans les communautés des Premières nations de l’Alberta où les taux de vaccination par le BCG sont faibles, le risque annuel d’infection est faible également, et le retrait du BCG ne pose pas de danger.
Footnotes
This study was presented in poster format to the International Union Against Tuberculosis and Lung Disease North American Regional meeting in Vancouver, February 24–26, 2005. p ]Supported by: First Nations and Inuit Health Branch, Alberta Region, and Alberta Health and Wellness.
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