The association of housing density, isolation and tuberculosis in Canadian First Nations communities

Michael Clarka, Peter Ribena and Earl Nowgesicb

a First Nations and Inuit Health Branch, Health Canada.
b Health Secretariat, Assembly of First Nations.

Michael Clark, Tuberculosis Program Officer, First Nations and Inuit Health Branch, Health Canada, PL 1920D, Tunney’s Pasture, Ottawa, Ontario, K1A 0L3, Canada. E-mail: Michael_Clark{at}hc-sc.gc.ca

Abstract

Background First Nations communities in Canada experience disproportionately high levels of overcrowded housing, degree of isolation, and rates of tuberculosis (TB). A study was done to assess the association between housing density, isolation, and the occurrence of TB in First Nations communities.

Methods Average persons per room (ppr), isolation type, average household income, population, and TB cases (1997–1999) at the community level were entered into a database. Tuberculosis notification rates and 95% CI were calculated for different strata of ppr and isolation. Two multiple logistic regression models were developed to examine the association of ppr, isolation, income, and population with the occurrence of >=1, or >=2, TB cases in a community.

Results The rate was 18.9 per 100 000 (95% CI: 13.3–24.6) in communities with an average of 0.4–0.6 ppr, while communities with 1.0–1.2 ppr had a rate of 113.0 per 100 000 (95% CI: 95.4–130.5). An increase of 0.1 ppr in a community was associated with a 40% increase in risk of >=2 TB cases occurring, while an increase of $10 000 in community household income was associated with 0.25 the risk, and being an isolated community increased risk by 2.5 times.

Conclusions This study shows a significant association between housing density, isolation, income levels, and TB. Overcrowded housing has the potential to increase exposure of susceptible individuals to infectious TB cases, and isolation from health services may increase the likelihood of TB.

Keywords Tuberculosis, housing, overcrowding, isolation, Aboriginal, Canada

Accepted 25 February 2002

In the early decades of the 20th century, the death rate from tuberculosis (TB) in the First Nations population of Canada was as high as 700 per 100 000. A combination of malnutrition, confinement on crowded reservations with poor sanitation, and lack of immunity to the TB bacillus contributed substantially to this epidemic.1 In 1999, the TB notification rate among First Nations people living on reserves in Canada was 10 times that of the overall Canadian rate in 1997.2

Overcrowded housing conditions can increase exposure of susceptible people to those with infectious respiratory disease, and in doing so may increase the probability of transmission. The association between overcrowded housing and TB incidence, paediatric TB, and TB mortality has long been recognized.3–5 Major housing problems have been identified in First Nations communities in Canada, and analyses have shown TB incidence is higher in communities isolated from health services.2,6 It has been widely stated that social conditions drive TB rates in Aboriginal communities upwards, but evidence for this relationship has been largely anecdotal and assumed to exist. This has led to a recommendation that this area be researched further.7–9 The purpose of this study is to examine the association between community housing density, isolation and the incidence and occurrence of TB in Canadian First Nations communities.

Methodology

Tuberculosis data by on-reserve community were provided by the seven First Nations and Inuit Health Branch (FNIHB) Regional TB programmes, which are responsible for TB control on reserves, for the period 1997–1999. The case definition for TB disease in Canada is standardized at the federal level, and used by each Regional programme. All forms of TB disease, including both pulmonary and extrapulmonary cases, were included in the analyses. The Canadian federal case definition is: (1) cases with Mycobacterium tuberculosis complex (i.e. M. tuberculosis, M. bovis [excluding BCG strain] or M. africanum) demonstrated by microscopy and/or on culture; or (2) in the absence of bacteriological proof, cases clinically compatible with active TB. The latter may include: chest X-ray changes compatible with active TB including idiopathic pleurisy with effusion; active extrapulmonary TB (meningeal, bone, kidney, peripheral lymph nodes, etc.); or pathological or post-mortem evidence of active TB.10 Population estimates and isolation types for on-reserve communities were obtained from the Community Workload Increase System (CWIS), a database used to estimate resource, funding and health programme needs in First Nations communities. Population figures were available for 1997. Isolation types are ‘remote isolated’ (no scheduled flights, minimal telephone and radio, no road access); ‘isolated’ (flights, good telephone service, no road access); ‘semi-isolated’ (flights, good telephone service, road access >90 km to physician services); or ‘non-isolated’ (flights, good telephone service, road access <90 km to physician services). Housing density and household income data by on-reserve community were available from the 1996 census, and were provided by Indian and Northern Affairs Canada (INAC). Housing density is expressed as the average number of persons per room (ppr) in a community, and household income is expressed in Canadian dollars. The ppr indicator for housing density has been used in other studies on the socioeconomic determinants of TB.3,5 All of these data were entered into a common database containing 602 community records. All associations analysed in the study were ecologic in nature, and not intended to establish causal links.

Tuberculosis incidence rates and 95% CI were calculated for different strata of community housing density and categories of isolation type. Confidence intervals for incidence were estimated using the formula:


Bivariate relationships between socioeconomic determinants were assessed using correlation analyses and t-tests. Correlation statistics were calculated for pairs of continuous variables (e.g. ppr and income), while t-tests were done to examine the difference in means of isolated versus non-isolated communities. The three isolation types other than ‘non-isolated’ were combined into a single ‘isolated’ category for t-tests and logistic regression analyses, because the number of people living in non-isolated communities is far greater than the number living in all other types combined.

Multiple logistic regression analyses were done to assess the association between potential predictors of TB in a community and the occurrence of >=1 case, and >=2 cases. The combination of TB, population, isolation, housing, and income data was available for 298 First Nations, on-reserve communities. A forward selection procedure was used, in which variables were entered into the model if P < 0.15, and taken out if P > 0.15. Hosmer and Lemeshow goodness-of-fit tests were done to assess the overall fit of the models to the data. All analyses were done using SAS 6.12 statistical software (SAS Institute, Cary, NC, USA).

Results

Descriptive statistics for TB, housing density, income and isolation are presented in Table 1Go. The 3-year, age-standardized TB notification rate (1997–1999) is eight times higher than the 1997 Canadian rate. Average housing density is higher in the First Nations, on-reserve population (0.7 ppr) than in the non-Aboriginal Canadian population (0.4 ppr). First Nations TB rates are highest in Saskatchewan, followed by Alberta and Manitoba. These three provinces also had the highest average levels of housing density. Income levels are lowest in the maritime provinces, similar to the trend in the non-Aboriginal population. Manitoba has the highest proportion of communities considered isolated (55.6%).


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Table 1 Age-adjusted tuberculosis (TB) notification rate (1997–1999), housing densities, household income (1996), and proportion of communities considered isolated, in Canada and in First Nations on-reserve population by province
 
The data available for different analyses are presented in Table 2Go. Tuberculosis and population data were provided for 602 First Nations communities. A code for isolation type was available for 576 (96%) of these communities. Due to lack of participation of many communities in the 1996 census, housing density and household income data were available for 474 (79%) and 298 (50%) of communities, respectively. The crude TB incidence rate among communities for which all types of data were available was 52.5 per 100 000 (95% CI: 47.1–57.9), significantly higher than the rate in all 602 communities of 37.7 per 100 000 (95% CI: 34.1–41.3).


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Table 2 Population and tuberculosis (TB) data available for analyses
 
Table 3Go shows TB notification rates by increasing levels of average ppr, grouped as 0.4–0.6, 0.7–0.9, 1.0–1.2, and 1.3+. During the period 1997–1999, the notification rate increased significantly as the level of housing density rises. The rate was 18.9 per 100 000 (95% CI: 13.3–24.6) in communities with an average of 0.4–0.6 ppr, while communities with 1.0–1.2 ppr had a rate of 113.0 per 100 000 (95% CI: 95.4–130.5), and communities with 1.3+ had a rate of 225.8 per 100 000 (95% CI: 137.3–314.3). Figure 1Go shows a relatively normal distribution of population by community housing density, and that TB incidence clearly rises as ppr increases.


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Table 3 Tuberculosis (TB) notification rate (per 100 000) and 95% CI, by strata of community housing density (1997–1999)
 


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Figure 1 Total population and tuberculosis (TB) notification rate by community housing density (1997–1999)

Bars represent population and line represents TB notification rates.

 
Tuberculosis incidence between 1997 and 1999 was significantly lower in non-isolated communities than in all categories considered isolated (Table 4Go). The rate in non-isolated communities was 20.0 per 100 000 (95% CI: 16.7–23.4), while rates for semi-isolated and isolated communities were 89.1 per 100 000 (95% CI: 69.4–108.7) and 89.6 per 100 000 (95% CI: 76.5–102.7), respectively.


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Table 4 Tuberculosis (TB) notification rate (per 100 000) and 95% CI, by community isolation type (1997–1999)
 
Correlation analyses showed that ppr and average household income were not significantly related (P = 0.59). A significant correlation was found between community population and ppr (P < 0.001), while population was not related significantly to income levels. T-tests indicated that mean persons per room and mean income levels were both higher in isolated communities than in non-isolated communities (P < 0.001).

Results of the two multiple logistic regression models are shown in Tables 5 and 6GoGo. In model 1 (Table 5Go), ppr and income level were not significantly related to the occurrence of >=1 TB cases in a community. An increase of 100 in community population was associated with a small increase in risk for TB (P = 0.0001), and being isolated was related to a twofold increase in risk (P = 0.0354).


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Table 5 Model 1: Association between community risk factors and presence/absence of one or more tuberculosis (TB) cases in a community (1997–1999)
 

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Table 6 Model 2: Association between community risk factors and presence/absence of >=2 tuberculosis (TB) cases in a community (1997–1999)
 
In model 2, all variables were significantly related to the occurrence of >=2 cases. In addition, the interaction of ppr and income was found to be a significant predictor. An increase of 0.1 ppr was associated with a 40% increase in risk of >=2 TB cases, while a $10 000 rise in community household income appeared to decrease risk by four times. Being an isolated community increased risk by 2.5 times. The goodness-of-fit statistics indicate that both models fit the data well (P = 0.99 and P = 0.84, respectively).

Discussion

In 1999, 40% of the total cases reported in the First Nations on-reserve population occurred in five communities.2 All of these communities were located in isolated areas, with average housing densities of >=8.0 ppr. Not all First Nations communities experience overcrowded housing and/or persistent TB outbreaks. This research attempts to increase understanding of what factors are associated with an increased risk in the minority of communities that did have a reported TB case between 1997 and 1999. The results suggest that TB incidence is higher in communities located in isolated areas, and in communities with a higher average housing density. The first of the two multivariate models (model 1) showed that isolation was associated with an increased risk of TB, while all predictors were significantly related to >=2 TB cases in model 2. It is possible that communities with >=2 cases experience higher transmission rates, and were more likely to be influenced by factors such as overcrowded housing.

Although an increase in community income was associated with a decreased risk of TB, income levels were higher in isolated communities where TB incidence is higher. This may be due to higher wages given to employees in isolated areas where the cost of living is elevated. The significant interaction between ppr and household income in model 2 may indicate that effect modification is present, and that housing density is associated with an increased risk of TB across different levels of income.

Some underlying factors that explain the occurrence of TB in certain communities were not considered in the multivariate models. For example, it is possible that communities with overcrowded housing also experience a higher prevalence of latent TB infection, and/or risk factors for progression from TB infection to disease. Such risk factors may include substance abuse,11 and undernutrition,12 which may be more prevalent in communities with socioeconomic disadvantages. Other socioeconomic variables associated with TB, such as unemployment and homelessness,13,14 were also neglected in the analysis due to lack of data. An ascertainment bias may have exaggerated the association between isolation and TB, as medical professionals in isolated communities where TB is endemic may be more likely to consider TB in their diagnoses. It is also possible that people in non-isolated communities are more likely to move off reserve, and may break down to disease in areas where FNIHB does not provide services. Despite these limitations, the data do support the conclusion that overcrowded living conditions and isolation from health services are associated with an increased risk of developing TB.

It has been hypothesized that the severity of the TB epidemic among First Nations after contact with Europeans was due more to social conditions such as crowding than the introduction of a more virulent strain of TB.15,16 In recent years, analyses have shown that clustering of culture-positive TB cases with the same DNA fingerprint is much more common in the First Nations population than in the non-Aboriginal Canadian population.17 The occurrence of these clusters, and high rates of TB infection and disease among children,2 show that First Nations likely experience an elevated risk of transmission, a risk that may be related to housing conditions. Overcrowded housing and inadequate community infrastructure have been associated with increased risk for other infectious diseases in First Nations populations, such as Shigellosis.18 The effect of overcrowding on TB epidemiology and control can be expressed in terms of its impact on the basic reproductive rate R0 of the disease over time. R0 is the average number of secondary infectious disease cases per infectious case.19 To reduce incidence of that disease and eventually achieve elimination, it is essential to bring R0 to <1 from year to year. Reducing the contact rate between infectious cases and other individuals generally has the effect of reducing R0, and contact rates decrease as socioeconomic conditions improve and overcrowding is prevented.20 The increased potential for contact due to overcrowding emphasizes the need to find and treat infectious TB cases in First Nations communities rapidly before transmission and clustering occur.

The association between poverty and TB is well documented.21,22 Barr et al. showed that neighbourhood poverty was associated with an increased risk of TB in New York City, adjusting for several other risk factors in a multivariate Poisson regression model.23 The results of this study show that increasing levels of income are associated with a reduced risk of TB in a community, and the combination of overcrowding and lower income levels may together increase risk of TB. It has been demonstrated that First Nations people with an annual income of <$10 000 are less likely to use health services than other income groups.24 Tuberculosis patient delays in presenting to health services are recognized as an important hindrance in finding and treating infectious TB cases before they spread the disease to others.25

The need to address overcrowded housing and other socioeconomic determinants of TB to eliminate TB in First Nations communities has been recognized.17 It may be beneficial to supplement traditional indicators of TB risk in a community, such as annual risk of infection and disease incidence,26 with the socioeconomic risk factors considered in this study. These indicators can be used by TB control programmes to assist community health staff in understanding risk for TB in the community, and to plan appropriate preventive actions based on this risk. The results also suggest that TB is more common in isolated communities, where unique challenges exist in transporting patients, equipment, drugs, and staff.


KEY MESSAGES

  • Overcrowded housing conditions can increase the occurrence of tuberculosis (TB) transmission from infectious to susceptible individuals.
  • Isolation from health services may lead to patient and provider delays in TB diagnosis, increasing the risk of transmission.
  • The Canadian First Nations population experiences higher housing densities and higher TB rates than the overall Canadian population.
  • Increased housing densities and geographical isolation have been associated with an increased risk of TB in Canadian, First Nations communities.

 

Acknowledgments

The authors wish to thank Indian and Northern Affairs Canada (INAC) for providing 1996 census data, the First Nations and Inuit Health Programs (FNIHB) Regional Tuberculosis Programs for their provision of TB data and ongoing efforts to eliminate TB, and the Assembly of First Nations (AFN) Information Governance Committee for supporting the study. The authors would also like to acknowledge Dr Shauna Hudson and Dr Pam Smith from FNIHB Saskatchewan Region, for their ideas and comments.

References

1 Wherrett GJ. The Miracle of Empty Beds: A History of Tuberculosis in Canada. Toronto: University of Toronto Press, 1977.

2 Health Canada. Tuberculosis in First Nations Communities, 1999. Ottawa: Minister of Public Works and Government Services, 2001.

3 Hawker JI, Bakhshi SS, Ali S, Farrington CP. Ecological analysis of ethnic differences in relation between tuberculosis and poverty. BMJ 1999;319:1031–34.[Abstract/Free Full Text]

4 Reinhard C, Paul WS, McAuley JB. Epidemiology of pediatric tuberculosis in Chicago, 1974 to 1994: A continuing public health problem. Am J Med Sci 1997;313:336–40.[CrossRef][ISI][Medline]

5 Elender F, Bentham G, Langford I. Tuberculosis mortality in England and Wales during 1982–1992: Its association with poverty, ethnicity and AIDS. Soc Sci Med 1998;46:673–81.[CrossRef][ISI][Medline]

6 Department of Indian Affairs and Northern Development. Basic Departmental Data, 1998. Ottawa: Minister of Public Works and Government Services Canada, 1999.

7 FitzGerald JM, Black WA, Kunimoto D. Evaluation of non-HIV-related, drug-sensitive cluster outbreaks of tuberculosis with PCR-based DNA fingerprinting. Can Respir J 1996;3:317–21.

8 Health Canada. Proceedings of the National Consensus Conference on Tuberculosis, 3–5 December 1997. Can Comm Dis Rep 1998;24S2:1–24.

9 Medical Services Branch. Tuberculosis Program and Epidemiologic Review. Ottawa: Minister of Public Works and Government Services, 1999.

10 Health Canada. Tuberculosis in Canada, 1998. Ottawa: Minister of Public Works and Government Services, 2001.

11 Reichman LB, Felton CP, Edsall JR. Drug dependence, a possible new risk factor for tuberculosis disease. Arch Intern Med 1979;139:337–39.[Abstract]

12 Palmer CE, Jablon S, Edwards PQ. Tuberculosis morbidity of young men in relation to tuberculin sensitivity and body build. Am Rev Tuberc 1957;76:517–39.[ISI]

13 Concato J, Rom WN. Endemic tuberculosis among homeless men in New York City. Arch Intern Med 1994;154:2069–73.[Abstract]

14 Brudney K, Dobkin J. Resurgent tuberculosis in New York City: human immunodeficiency virus, homelessness, and the decline of tuberculosis control programs. Am Rev Respir Dis 1991;144:745–49.[ISI][Medline]

15 Ferguson RG. Tuberculosis among the Indians of the Great Canadian Plains. Preliminary report of an investigation being carried out by the National Research Council of Canada. London: Adlard and Son,1929.

16 Clark GA, Kelley MA, Grange JM, Hill MC. The evolution of mycobacterial disease in human populations: a reevaluation. Curr Anthropol 1987;28:45–62.[CrossRef][ISI][Medline]

17 FitzGerald JM, Wand L, Elwood RK. Tuberculosis: 13. Control of the disease among Aboriginal people in Canada. Can Med Assoc J 2000; 162:351–55.[Abstract/Free Full Text]

18 Rosenburg T, Kendall O, Blanchard J, Martel S, Wakelin C, Fast M. Shigellosis on Indian reserves in Manitoba: Its relationship to crowded housing, lack of running water, and inadequate sewage disposal. Am J Public Health 1997;87:1547–51.[Abstract]

19 Anderson RM, May RM. Infectious Diseases of Humans: Dynamics and Control. Oxford: Oxford University Press, 1991.

20 Vynnycky E, Fine PEM. Interpreting the decline in tuberculosis: the role of secular trends in effective contact. Int J Epidemiol 1999;28:327–34.[Abstract]

21 Spence DPS, Hotchkiss J, Williams CSD, Davies PDO. Tuberculosis and poverty. BMJ 1993;307:759–61.[ISI][Medline]

22 Drucker E, Alcabes P, Bosworth W, Sckell B. Childhood tuberculosis in the Bronx, New York. Lancet 1994;343:1482–85.[ISI][Medline]

23 Barr RG, Diez-Roux AV, Knirsch CA, Pablos-Méndez A. Neighborhood poverty and the resurgence of tuberculosis in New York City, 1984–1992. Am J Public Health 2001;91:1487–93.[Abstract/Free Full Text]

24 Waldram JB, Herring DA, Young TK. Aboriginal Health in Canada: Historical, Cultural, and Epidemiological Perspectives. Toronto: University of Toronto Press, 1995.

25 Rieder H. Case finding in high- and low-prevalence countries. In: Reichman LB, Hershfield ES (eds). Tuberculosis: A Comprehensive International Approach. 2nd Edn. New York: Marcel Dekker, 2000, pp. 323–39.

26 Enarson DA, Rouillon A. The epidemiological basis of tuberculosis control. In: Davies PDO (ed.). Clinical Tuberculosis. 2nd Edn. London: Chapman & Hall, 1998, pp. 35–52.