Africa's most populous nation, Nigeria, also has the world's 6th highest number of citizens going to the bathroom outside. Of 151 million people living in Nigeria, 33 million do it in the open. Still, more than 12 million people there have gained access to sanitation facilities over the past two decades.
Across Sub-Saharan Africa over the past two decades, the number of people not using sanitary facilities fell 25 percent, according to the WHO's 2010 update (pdf).