Use of geographic and genotyping tools to characterise tuberculosis transmission in Montreal
OBJECTIVES: To detect spatial aggregation of cases, areas of excess incidence and local ‘hot spots’ of transmission in Montreal.
DESIGN: We used residential addresses to geocode active TB cases reported on the Island of Montreal in 1996–2000. After a hot spot analysis suggested two areas of overconcentration, we conducted a spatial scan, with census tracts (population 2500–8000) as the primary unit of analysis and stratification by birthplace. We linked these analyses with genotyping of all available Mycobacterium tuberculosis isolates, using IS6110-RFLP and spoligotyping.
RESULTS: We identified four areas of excess incidence among the foreign-born (incidence rate ratios 1.3–4.1, relative to the entire Island) and one such area among the Canadian-born (incidence rate ratio 2.3). There was partial overlap with the two hot spots. Genotyping indicated ongoing transmission among the foreign-born within the largest high-incidence zone. While this zone overlapped the area of high incidence among Canadian-born, genotyping largely excluded transmission between the two groups.
CONCLUSIONS: In a city with low overall incidence, spatial and molecular analyses highlighted ongoing local transmission.
Document Type: Regular Paper
Affiliations: 1: Department of Geography, McGill University, Montreal, Quebec, Canada 2: Division of Medical Microbiology and Infectious Diseases, McGill University, Montreal, Quebec, Canada; and Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada 3: Respiratory Epidemiology Unit, McGill University, Montreal, Quebec, Canada; and Department of Epidemiology and Biostatistics, McGill University, Montreal, Quebec, Canada 4: Laboratoire de Santé Publique du Québec, Montreal, Quebec, Canada 5: Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada; and Division of Clinical Epidemiology, McGill University, Montreal, Quebec, Canada 6: Respiratory Epidemiology Unit, McGill University, Montreal, Quebec, Canada; and Respiratory Division, McGill University, Montreal, Quebec, Canada
Publication date: 2007-06-01
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