Environmental Determinants of Tuberculosis

Tuberculosis (TB) is an infectious disease caused by the aerobic, non-motile bacillus Mycobacterium tuberculosis (M.TB) (Robbins, Cotran, Kumar & Collins 1999). The lipid capsule of the bacterium causes chronic granulomatous infections, primarily in the lungs but able to disseminate to most other bodily organs (Robbins et al. 1999). TB is a treatable disease which is still causing fatalities, and some parts of the world have begun to see the emergence of multi- and extremely drug resistant strains of M.TB (Dye, Scheele, Dolin, Pathania & Raviglione 1999; Singh, Upshur & Padayatchi 2007). Environmental factors playing a role in TB transmission can be classified into factors affecting the natural, social, political or economic environments. It is important to keep in mind that these classifications are solely for the ease of discussion; in reality, factors cannot be discretely classified, for example, social factors are often affected by politics and economics.

The natural environment can be further subdivided into the domestic environment, the environment in institutions such as hospitals, and environmental factors which affect entire population groups. TB is transmitted in aerosolised sputum particles whenever an infected person coughs (Robbins et al. 1999), therefore crowded domestic environments have been identified in several studies as promoting TB transmission since there is physical proximity to infected individuals (American Nurses Association 2006; Canadian Tuberculosis Committee2007; Filipov 2003; Lillebaek 2005; van der Eijk, van de Vosee, Vandenbroucke & van Diesel 2007). Living in confined spaces also increases the risks of transmission because droplet concentrations in air are increased. (American Nurses Association 2006; Jensen, Lambert, Iademarco & Ridzon 2005). Shelter with inadequate ventilation and long periods of exposure to infectious people also increases TB transmission. Besides poor design or quality housing, the Canadian Tuberculosis Committee (2007) identifies temperature extremes, environmental noise, energy costs and the use of indoor heating such as wood burning stoves as factors which contribute to the inhibition of adequate ventilation, and therefore promote TB transmission. This report also identified poor domestic air quality, which can be caused by wood fires or stoves, smoking, mould or general environmental air pollution, as a factor increasing the risk of TB transmission, since all these things adversely affect respiratory health and therefore make individuals more likely to contract TB. All of the above domestic environmental factors are controllable by improving housing standards and patient education.

Environmental factors within institutions such as hospitals, homeless shelters and prisons, which play roles in the transmission of TB include the recirculation of air within the institution, lack of isolation policies for infectious patients, inadequate disinfection of equipment, improper specimen handling practices and procedures which cause expulsion of, or exposure to, large amounts of potentially infected sputum or other body secretions, for example, bronchoscopy, chest drains and induced sputum collections (American Nurses Association 2006; Canadian Tuberculosis Committee2007; Jensen et al. 2005). Rather than recirculating air within an institution, especially hospitals, technologies which promote ventilation can be used so as to prevent the dissemination of TB nosocomially. These technologies include general ventilation techniques, such as opening as many windows as possible, and other technologies such as the installation of laminar air flow systems, high efficiency particulate air filters, negative pressure isolation rooms, ultraviolet gamma irradiation of used air and the use of protective respirators by staff and visitors of TB patients (American Nurses Association 2006; Jensen et al. 2005). Further public health methods to reduce this sort of TB transmission include the implementation and regular monitoring of TB control programs within institutions, effective contact tracing, staff education on the methods of nosocomial transmission, regular reviews of disinfection and equipment sterilisation measures and a clear triage policy relating to patients with sputum positive TB (Jensen et al.2005). Subject to local legislation, many prisons and hospitals may require to review their standing as regards isolation of identified sputum positive TB cases from the general institutional population. This issue does however raise many ethical questions. One way for hospitals to solve the associated ethical dilemmas is to have separate infectious diseases or tuberculosis wings, or even separate hospitals specialising in TB management.

Environmental factors which affect entire groups of or within the population often overlap with social factors, such as crowding within reserves where mostly indigenous populations live, prisons or refugee camps (Canadian Tuberculosis Committee2007; Filipov 2003; Lillebaek 2005).An important population factor which can also be considered as a host factor is the population’s levels of immunocompromised individuals. Although HIV is the commonest immunocompromised state associated with increased rates of TB transmission, any other major chronic diseases prevalent, such as diabetes, cancers, cardiac disease, asthma, and other respiratory infections, predispose the population to higher TB transmission rates (Canadian Tuberculosis Committee2007; Dye et al. 1999; Geiter 2000; Jensen et al 2005).Bany & Freier (2000) identified proximity to wildlife reserves which can act as reservoirs for mycobacteria as an environmental factor leading to repeated outbreaks of TB in Molokai.

Social environmental factors include living within indigenous communities, especially in reserves (Canadian Tuberculosis Committee 2007; Wobeser, Yuan, Naus, Corey, Edelson, Heywood & Linn Holness 2000), as well as immigrant or refugee communities (Canadian Tuberculosis Committee2007; Wobeser et al 2000). This is because these communities are socially disadvantaged and often have poor housing and living conditions, and many refugees or immigrants come from countries with high TB prevalence. Incarceration and homelessness are two social states which provide similarly poor quality of housing and thus predispose these individuals to acquiring TB (Geiter 2000; Wobeser et al 2000). Wobeser et al (2000) report that marital status also plays a role in TB transmission, with single, divorced or widowed people more likely to acquire TB than married couples. Compliance to treatment has been identified as an important way of breaking the transmission cycles of TB, and non-compliance increases the chances of transmitting TB, and acquiring drug resistant forms of the bacillus (Filipov 2003;Munro, Lewin, Smith, Engel, Fretheim & Volmink n.d.; Singh,Upshur & Padayatchi 2007; World Heath Organisation 2001). Social factors which may lead to non-compliance include social stigma attached to a diagnosis of TB (Munro et al n.d., Singh,Upshur & Padayatchi 2007) and lack of community or household support for treatment programs. (Munro et al n.d.).

Factors from the political environment include legislation relating to refugee and migrant screening and detention (Geiter 2000; Wobeser et al 2000), the treatment of ethnic minorities (Canadian TuberculosisCommittee 2007) and legislation on indigenous peoples’ rights, especially to land (Canadian Tuberculosis Committee 2007). Political rulings about the funding and control of TB control and treatment programs also affect transmission, as these rulings affect the ability of programs to carry out education, treatment and prevention of TB (Singh,Upshur & Padayatchi 2007). Filipov (2003) highlights that centralised policies may be better than decentralised policies in controlling TB transmission, by giving the example of the Soviet Union’s excellent TB control versus Russia’s burgeoning drug resistance problems. The World Health Organisation branch in Thailand (2001) identifies the importance of political regulation of pharmaceutics in preventing transmission of multi-drug resistant TB in particular. Another political factor that can increase TB transmission is the out break of wars, as these drop living conditions and hinder TB programs from doing their work (Lillebaek 2005).

The major factor from the economic environment which plays a role in TB transmission is poverty (Filipov 2003;Gupta,Das,Balamugesh,Aggarwal & Jindal 2004; Jensen et al 2005; Lillebaek 2005; Munro et al n.d.; Singh,Upshur & Padayatchi 2007; WHO 2001; Wobeser et al 2000). Poverty affects most of the other factors discussed so far from all the other environmental classifications. Poverty causes a low socio-economic status (Gupta et al 2004; Wobeser et al 2000) which often exposes individuals to crowding in low quality housing, unemployment, homelessness, incarceration, negative social attitudes that can form a barrier to seeking treatment at institutions such as hospitals and social stigma. Certain ethnicities are more likely to suffer from poverty, namely indigenous populations and immigrants (Canadian Tuberculosis Committee2007).Poorer countries have less stable drug supplies and drug interruptions lead to poor compliance and increased transmission rates of TB and the emergence of drug resistant strains (Filipov 2003; WHO 2001).Poorer individuals in any country have less disposable income to spend on the 6-8 month long course of drugs needed to treat TB, and many may be unable to access TB programs due to the need to work maximum hours in order to make ends meet (Munro et al n.d.). Economic inequalities among genders in some cultures mean that women are less likely to get adequate treatment and therefore transmission increases, because women are dependant on familial support to pay for treatment (Munro et al n.d.).

Thus it is clear that public health policies need to tackle the issue of poverty, and attempt to improve the economic circumstances of individuals. It is only by amassing enough social and political will to minimise poverty that there will be any real and perhaps lasting effect made on the rates of transmission of TB worldwide, since so many of the environmental factors affecting TB transmission have their roots in social, political and economic factors. In Australia, TB control needs to remain a topic of importance since Australia has growing numbers of immigrants and refugees as well as a vulnerable Aboriginal population, and since Australia is not immune to the urban poverty which is increasing with the prevailing economic climate worldwide.