INTRODUCTION During 1950-2008, the proportion of the world's population living within cities grew from 33% to 50% (1). The number of cities with 10 million people grew from 3 to 20 over the past 30 years; 15 of these 'megacities' were in the developing world (1). The urban population in sub-Saharan Africa is expected to triple between 2010 and 2050 to 1.2 billion people (2). This process of massive urbanization has been ongoing in many developing countries, including in sub-Saharan Africa where urbanization rates, often linked to extreme poverty (3), are the highest in the world (4). Perceived opportunities for improving the family status and for education have led many people to leave rural settings in favour of urban living environments which can be more challenging and less familiar (5). Since urban areas often cannot address the demands of an expanding population with strengthened infrastructure, the new residences are frequently seen within informal settlements, often referred to as slums, where the density of population is high, and sanitation, availability of clean water, and health services are low (5).
