Serious infections in patients with myasthenia gravis: population-based cohort study.

BACKGROUND AND PURPOSE: To characterize the frequency and risk of serious infections in patients with myasthenia gravis (MG) relative to age/sex/area-matched comparators. METHODS: This was a population-based cohort study in Ontario, Canada of patients with newly-diagnosed MG and 1:4 age/sex/area-matched general population comparators accrued from 1 April 2002 to 31 December 2015. The main outcome was a serious infection, defined by a primary diagnosis code on a hospitalization or emergency department record. We computed crude overall and sex-specific rates of infection among patients with MG and comparators, and the frequency of specific types of infection. Adjusted hazard ratios and 95% confidence intervals were estimated using Cox regression. RESULTS: Among 3823 patients with MG, 1275 (33.4%) experienced a serious infection compared with 2973/15 292 (19.4%) of comparators over a mean follow-up of over 5 years. Crude infection rates among patients with MG were twice those in comparators (72.5 vs. 35.0 per 1000 person-years, respectively). The most common infection types were respiratory infections, particularly bacterial pneumonia. After adjustment for potential confounders, MG was associated with a 39% increased infection risk (adjusted hazard ratio, 1.39; 95% confidence intervals, 1.28-1.51). CONCLUSIONS: Patients with MG are at a significantly higher absolute and relative risk of serious infections compared with age/sex/area-matched comparators. This needs to be considered when selecting MG treatments and when planning vaccination/prophylaxis. Determining whether this risk is due to the use of immunosuppressive medications (vs. MG itself) is an important area for future research.

Estimating chronic disease rates in Canada: which population-wide denominator to use? / Taux de maladies chroniques au Canada : quel dénominateur utiliser pour l'estimation de l'ensemble de la population?

INTRODUCTION: Chronic disease rates are produced from the Public Health Agency of Canada's Canadian Chronic Disease Surveillance System (CCDSS) using administrative health data from provincial/territorial health ministries. Denominators for these rates are based on estimates of populations derived from health insurance files. However, these data may not be accessible to all researchers. Another source for population size estimates is the Statistics Canada census. The purpose of our study was to calculate the major differences between the CCDSS and Statistics Canada's population denominators and to identify the sources or reasons for the potential differences between these data sources. METHODS: We compared the 2009 denominators from the CCDSS and Statistics Canada. The CCDSS denominator was adjusted for the growth components (births, deaths, emigration and immigration) from Statistics Canada's census data. RESULTS: The unadjusted CCDSS denominator was 34 429 804, 3.2% higher than Statistics Canada's estimate of population in 2009. After the CCDSS denominator was adjusted for the growth components, the difference between the two estimates was reduced to 431 323 people, a difference of 1.3%. The CCDSS overestimates the population relative to Statistics Canada overall. The largest difference between the two estimates was from the migrant growth component, while the smallest was from the emigrant component. CONCLUSION: By using data descriptions by data source, researchers can make decisions about which population to use in their calculations of disease frequency.

INTRODUCTION: Les taux de maladies chroniques du Système canadien de surveillance des maladies chroniques (SCSMC) de l'Agence de la santé publique du Canada sont fondés sur les données administratives sur la santé fournies par les ministères de la Santé des provinces et des territoires. Les dénominateurs utilisés pour calculer ces taux reposent sur des estimations de population tirées des dossiers d'assurance-maladie, données toutefois pas systématiquement accessibles à tous les chercheurs. Le recensement de Statistique Canada constitue quant à lui une autre source d'estimation de la taille de la population. Notre étude visait d'abord à calculer les principaux écarts entre les dénominateurs de population à partir des estimations du SCSMC et à partir de celles de Statistique Canada et ensuite à déterminer les causes à l'origine des écarts entre ces sources de données. MÉTHODOLOGIE: Nous avons comparé pour 2009 les dénominateurs fournis par le SCSMC et ceux fournis par Statistique Canada. Le dénominateur du SCSMC a été ajusté pour tenir compte des composantes de la croissance (naissances, décès, émigrants et immigrants) tirées des données de recensement de Statistique Canada. RÉSULTATS: Le dénominateur non ajusté du SCSMC était de 34 429 804 personnes, soit une différence de + 3,2 % par rapport à l'estimation de population de Statistique Canada pour 2009. Après ajustement du dénominateur du SCSMC pour tenir compte des composantes de la croissance, la différence entre les deux estimations s'est trouvé réduite à 431 323 personnes, soit un écart de 1,3 %. L'estimation tirée du SCSMC constitue une surestimation par rapport à celle de Statistique Canada. Le plus grand écart entre les deux estimations relève de la composante de croissance liée à l'immigration, alors que l'écart le moindre provient de la composante de croissance liée à la population émigrante. CONCLUSION: Disposant des descriptions de données par source de données, les chercheurs peuvent choisir quelle estimation de la population utiliser dans leurs calculs des fréquences de maladies.