While the overall annual incidence of tuberculosis (TB) on the Island of Montreal has been stable at 10 per 100,000 in recent years, incidence varies tremendously by country of birth and by neighbourhood. It is not clear how much of this variation reflects population distribution, and how much reflects localized risk factors and/or local transmission. Precise mapping and spatial statistical analysis allowed for the iden­tification of two types of TB concentrations: hotspots - raw concen­trations of cases, and high-incidence zones - where TB incidence significantly exceeds the rate expected....