Tuberculosis in Montreal

The association of tuberculosis (TB) with poverty has long been recognized, yet it may reflect not only characteristics of poor individuals, but also housing and neighborhood features which promote airborne spread. It is determined whether dwelling and building features, residential density and crowding are independently associated with TB occurrence in a low-incidence setting. A residential addresses to geocode active TB cases reported in Montreal in 1996–2000. These ‘‘case dwellings’’ were linked to the municipal dwelling geodatabase from 2000, and to Canadian census data from 1996. We compared them with randomly selected Montreal dwellings (‘‘controls,’’ in a 1:10 ratio), using the same data sources. From multivariate logistic regression, the 595 case dwellings were more likely than the 5950 control dwellings to be in buildings 45 stories tall (adjusted odds ratios [OR] 1.6; 95% CI: 1.0–2.5), constructed since 1970 (adjusted OR 2.5; 1.8–3.6), in the lowest quartile for resale valuation (adjusted OR 1.3; 1.0–1.6), and on blocks where lot coverage exceeded the median value (adjusted OR 1.3; 1.0–1.6). Case dwellings were also more often found in census tracts with more persons per room, and a higher proportion of inhabitants who had arrived in Canada within the last 5 years.

Tuberculosis
The association of tuberculosis (TB) with poverty has long been recognized (Elender, Bentham, & Langford, 1998; Mangtani, Jolley, Watson, & Rodrigues, 1995). This may reflect not only medical and social characteristics of poor individuals, but also characteristics of housing and neighborhood which foster airborne spread of tuberculous infection, such as crowding and poor ventilation. Population groups with an increased prevalence of latent TB infection (such as new immigrants) are disproportionately found in poor areas—often with lower quality, more crowded housing. Crowding and poor ventilation also increase the probability of inhaling bacilli expelled by infectious individuals. Persons at increased risk of active disease following such exposure (e.g. HIV-infected persons) may also be disproportionately located in poor areas.

In Canada
In Canada as in other industrialized countries, TB is increasingly concentrated in the largest cities (Long, Njoo, & Hershfield, 1999). This reflects the preponderance of foreign-born persons—particularly new arrivals—and the importance of urban risk factors such as homelessness, substance use, and HIV infection. Montreal is Canada’s second largest city, and TB incidence varies tremendously by neighborhood; when described by community clinic catchment area, estimated incidence ranged from 3.1 per 100,000 (middle-class suburbs 20–30km west of the city center) to 40.0 cases per 100,000 (a poor area with many foreign born, located due north of downtown) during 1995–98 (Rivest, Tannenbaum, & Bédard, 1998). Much of this variation reflects individual sociodemographic characteristics, but may also reflect differences in housing or other neighborhood characteristics. Montreal has more residential segregation by income than most large Canadian cities—though much less so than many US cities (Ross, Houle, Dunn, & Aye, 2004; Ross, Nobrega, & Dunn, 2002).

City of Montreal
The City of Montreal accounted for 57% of the population of the Island of Montreal, and 73% of TB cases.

The Canadian census is conducted every 5 years. We used 1996 census data to characterize the 395 census tracts within the City of Montreal. The census tract is the lowest level of data reporting for most socioeconomic and demographic variables; demographic variables such as country of origin are based on a 20% sampling frequency, and are aggregated to the census tract level to ensure confidentiality and statistical precision.