The first paper in this Series was concerned with health in slums and with the determinants of health.1 We noted that the intimately shared physical and social environment in slums is likely to generate strong neighbourhood effects. In this second paper, we consider what can be done to improve health and health care in slums and show how factors operating at the neighbourhood level can be turned to advantage when we intervene. We start by discussing general epidemiological principles that should be taken into account in interpreting the results of studies in slums. Next, we describe an intellectual framework to organise evidence on interventions. We then present such evidence as we were able to glean according to this intellectual framework. Lastly, we discuss the implications of the findings from this Series as a whole for policy and research.
Three factors interact to determine how an intervention can play out in slum neighbourhoods. First, densely packed slum neighbourhoods promote the spread of disease but also provide opportunities for economies of scale when interventions are promulgated. An iconic example is the dramatic effect John Snow achieved when he aborted a cholera epidemic by disenabling a water pump in Soho, London in 1854.
Second, we showed in paper one that slums are not homogeneous, but present very different social and physical environments. Context should therefore be taken into account when interpreting the results of intervention studies. For example, the effect of raising the floors of slum dwelling to reduce contamination from the surroundings may have a much smaller effect on rates of childhood diarrhoea if water supply and sewage disposal have been upgraded than if they have not.
Key messages
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The neighbourhood effects in slums are likely to offer economies of scale and increasing returns to investments to create a healthy environment
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Although relocation and resettlement can be necessary for safety reasons, slum upgrading in situ is usually preferable to improve the health and welfare of people living in slums
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Sanitation, which started the public health revolution in Europe and America during the 19th century, remains a key neighbourhood challenge in slums
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Health services should be designed specifically to overcome barriers to utilisation, such as distance and cost, for people who live in slums
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Health services should be proactive in health protection—eg, by immunisation and surveillance for childhood malnutrition
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People who live in slums and their organisations should have an active say in the prioritisation, design, implementation, and evaluation of interventions in slums
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Slum enumeration areas should be identified in all census listings and sampling frames to enable clearer understanding of the neighbourhood effects of slums
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Enabled by this spatial construct, much more research is needed on slum health and how to improve it, and a greater proportion of this research should be based on multicentre studies with contemporaneous controls
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Finally, we advocate the development of capacity for research into slum health and the emergence of this as an academic specialty
And finally, the relationship between dose and response must be considered. This relationship may be non-linear, especially in dynamic scenarios where one person's risk affects another person's risk, either because the disease is infectious, or because one person's behaviour influences the health of others. In such a scenario, increasing returns on investment are likely. An example that we will discuss later concerns provision of sanitation which is likely to exhibit increasing returns to scale as faecal contamination is progressively reduced. Failure to realise the steep part of the curve by supplying sanitation at insufficient scale or intensity might explain why many sanitation improvement projects have yielded disappointing results and point the way for development and evaluation of more intense interventions.
In figure 1, we model the ways that context and dose-response correlations can interact.
We organised our analysis using a generic three level causal model2, 3 that has been applied in previous research of slum upgrading4 and in a Cochrane Review of this topic.5 Figure 2 shows these three levels. The first or macro-level is constituted of institutions and policies affecting all citizens, including press freedom, an independent judiciary, monetary and fiscal policy, and other national or supranational influences. Second is the middle or meso-level relating to slum specific policies. These policies, such as those for land zoning and provision of tenure, set the context where targeted interventions, such as improved sanitation, play out. It is therefore referred to as the enabling layer in the Cochrane Review.5 And finally, the micro-level encompassing interventions targeted at specific problems such as faecal contamination of the environment; referred to as the direct level in the Cochrane Review.
We will not consider the first (macro) level because it concerns politics and economics and although these are important influences on health, much can be done to improve health pending an improved macro-economic environment.7, 8 Massive gains in health have been recorded even in countries with poor national governance9 and it is worth reflecting that infant mortality in slums is currently about 46 per 1000 livebirths,10 whereas in Victorian England (1837–1901) the upper class infant mortality rate in 1899 was three times higher (136 per 1000).11 The search strategy and selection criteria panel shows how we searched for key literature on interventions to improve slum health.
