As far back as the days of the Greek empire it was understood that the built environment played a significant role in public health. This agenda was one of the main drivers of early town planning practice, and is still a major concern today. Recent literature on the developed world focuses on the link between obesity and the physical environment, and literature on the developing world continues the historical focus on the link between adequate sanitation and the prevention of waterborne illnesses.
However, what has mostly been omitted from this discussion, at least on the part of built environment professionals, is the link between the built environment and tuberculosis (TB). This is highly problematic since 19% of total global TB burden is attributable to environmental factors, according to the World Health Organisation. Ignoring this link is particularly problematic in South Africa where TB is the leading cause of death, and TB and HIV/AIDS is the leading cause of premature death for those between 1 and 50-years-old, according to data from Humanosphere (see graph below).
The link between TB and the built environment has a relatively long history. In the developed world, the major reductions in TB prevalence were due firstly to improvements in housing and public health, not antibiotics (1, 2 and 3).
In South Africa, more recent work has shown that increasing ventilation can have a substantial effect on reducing the likelihood of TB transmission. In their study, Melissa Lygizos and colleagues looked at traditional houses in KwaZulu-Natal. They found that when doors and windows were opened in the houses studied the estimated TB transmission risk dropped from 55.4 percent to 9.6 percent.
The question is then: what can African built environment practitioners do to create housing that reduces the likelihood of TB transmission? Research on this topic is limited but there are a number of actions that could assist in improving housing conditions:
- Reduce overcrowding: Bart Willems, previously a registrar in Public Health at the University of Stellenbosch, indicates that the issue is one of room occupancy and volume. “An increase in number of people in the room increases the risk of TB transmission,” he told me in written correspondence. “The volume of the room (bigger volume is better) and an increase in the number of air changes per hour (per person) can reduce the risk of transmission.”
In terms of data from Census 2011, we know that 7.28 percent of households in South Africa have a room occupancy rate of 2.5 people. This indicates that around a fourteenth of households in South Africa are overcrowded, using a measure of more than 2 persons per room, and vulnerable to TB infection should any one member of the household contract TB.
- Design homes for low-income households that use natural ventilation: There is a considerable body of work on how to achieve this. The challenge in South Africa is how to design a house that is well ventilated and cooler in the hotter months, but also able to maintain this ventilation in the cooler months without lowering the house temperature below uncomfortable levels. Ideally, what is required is a cost-effective, mixed natural and mechanical ventilation system that allows for cooling in summer and warming of air in winter, and does not mix incoming and outgoing air. While systems already exist that meet some of the aforementioned criteria (see for example Breathable Buildings) no system, to my knowledge, meets all of them. This is an area that requires urgent product research.
- Ensure that houses have ample indoor exposure to sunlight: Sunlight potentially has two effects on the incidence of TB. Firstly, direct sunlight kills TB bacteria. Secondly, sunlight is important for maintaining high Vitamin D levels, which in some studies have been associated with a lower rate of TB symptoms. Given this, it is recommended that houses be designed to maximize solar exposure.
- Improve the quality and size of low-income housing: In correspondence with Dr. Jo Barnes, a lecturer at the University of Stellenbosch, Department of Community Health, she indicated that work she has done, looking at low-cost houses in Cape Town, has shown that many of those living in the households in the study area block off the air flowing through their houses. She was of the opinion that this happens for two reasons, namely the “obvious lack of space in these small, overcrowded houses and inability to keep them warm in winter.” She continues, “The houses are built of cement bricks and not plastered or painted in most cases. The walls absorb rainwater and act like a cold room structure when the wind blows on the wet walls. In most cases the walls are so wet in winter that free water runs down the insides of the walls. Such damp also acts as another risk factor for the transmission of TB.”
- Lay out streets and plots in a pattern that maximizes wind flow and solar exposure: Some of the oldest guidance on street layout promotes orientation of streets in such a manner that wind is dissipated. The goal with developing housing and settlements that are resistant to tuberculous is the opposite, specifically to maximize wind flow. The two components of street layout that affect wind flow are orientation and width. The orientation of the streets should typically be 300 to the dominant wind direction, but the resulting design must ensure that the plots can optimally allow houses to have the long axis running east-west so as to enable optimal solar exposure. In addition, in settings with tall buildings the street width should be 0.3-0.7 times the height of the building, in order to encourage a faster wind speed.
Achieving the above will not be easy, given the impracticality of providing free houses to all poor South African households, and the low incomes of these households. This does, however, challenge us as built environment practitioners to consider how these targets could be met, for example, by building low-cost, high-quality homes using earth and waste materials (see from Trash to Treasure).
The achievement of building low-income houses in South Africa that reduce the likelihood of TB transmission, and in the process also reduce the impact of air pollution on households, is one of the most important challenges facing built environmental professionals in Southern Africa.
A word of thanks to Doctors Katrina du Toit, Koot Kotze, Helene-Mari van der Westhuizen, Jo Barnes and Bart Willems for providing guidance and insight into this topic.
Stuart Denoon-Stevens is a professional planner, a junior lecturer at the University of the Free State, and a researcher focusing on municipal land management, with a particular emphasis on pro-poor approaches.
Photo credit: Brendon Bosworth
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