In consequence, the number of urban dwellers practising open defecation increased from 140 million to 169 million between 1990 and 2008.47 The impact of this practice in densely populated urban settlements is particularly alarming for public health. Congested and unsanitary conditions make urban slums particularly high-risk areas for communicable diseases, including cholera. Yet patterns of deprivation differ. While Blantyre exhibits greater levels of poverty than adjacent areas, Lilongwe is a relatively well-off urban centre surrounded by poorer regions, but also showing pockets of poverty (isolated darker areas) within its limits.