Here’s a troubling report (from 2009) from Oxfam on Nairobi’s urbanization

“The scale of urban poverty in Kenya is something that policymakers can no longer afford to ignore. Between a third and half of the country’s urban population live in poverty. The country is urbanising at such a speed that it is projected to be 50 per cent urban by 2020, and half of all Kenya’s poor will be living in urban areas. In this respect there can be no doubt that poverty itself is rapidly urbanising in Kenya.
Oxfam GB Kenya’s report highlights the mutually reinforcing dimensions of vulnerability in Nairobi’s slums, including the following:

• Urban residents are almost twice as likely to be infected with HIV as their rural counterparts
• Children in Nairobi’s slums are among the unhealthiest in the country. Over half are likely to suffer acute respiratory infection and almost half under 5 are stunted; moreover they are less likely to be immunised than children elsewhere in Kenya and more prone to diarrhea and fever.”