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Environmental Determinants of Tuberculosis

Tuberculosis is a worldwide disease that annually claims millions of lives. What are th environmental factors that have been proved to assist in its transmission?

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.

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