There is still one subject in international development that goes unmentioned. It is an issue that touches on the lives and health of millions of individuals, and one which world leaders have promised to address.
Sanitation is one of the last remaining taboos, but today a staggering 2.6 billion people have no access to a safe, hygienic toilet.
This week heads of state will meet at the UN for an historic meeting, where they will discuss and plan how to keep their promises set out ten years ago in the Millennium Development Goals (MDGs).
These ambitious goals were set out to halve the proportion of people living in extreme poverty and world leaders committed to "making the right to development a reality for everyone and to freeing the entire human race from want."
With just five short years remaining until these promises are due to be met, several remain off track. It is not surprising that sanitation, one of the least talked about development interventions, is one of the most off track MDG targets.
Initially ignored, a target on sanitation was agreed two years after the others were set when it became clear that efforts to improve access to clean drinking water would not succeed without commensurate efforts to improve access to sanitation.
Diarrheal diseases caused by poor sanitation and dirty water kill more children than AIDS, malaria and measles combined. In Africa, where the goals are most off-track, diarrhea is now the biggest killer of children. At current rates of progress the target to halve the people without access to an adequate toilet will not be met globally until 2049; in Sub-Saharan Africa not until the 23rd century, some 200 years late.
Yet nine out of ten cases of diarrhea can be prevented by safe sanitation, hygiene and water. Access to sanitation also significantly reduces other leading causes of child deaths, such as undernutrition and pneumonia.
Sanitation is intimately linked with all areas of human development addressed by the MDGs. An estimated 443 million school days are lost each year due to illness caused by poor sanitation and water, with long-term repercussions on educational attainment and economic growth. And at any one time, half of all hospital beds in developing countries are filled with people suffering from water- and sanitation-related diseases, burdening health systems that are struggling to cope and costing approximately 12% of public health spending in Sub-Saharan Africa.
Women and girls are particularly vulnerable. They may face violence, sexual assault and other dangers such as snake or crocodile attacks when walking long distances for water or when they can only defecate outside and after dark. Without toilets, girls often drop out of school, especially when menstruating. In many societies, women and girls perform most of the unpaid labour that comes with providing water for their families, leaving less time for education and paid employment, and perpetuating gender inequality.
This is a vicious cycle - of poverty, ill health and disempowerment - and it is a silent cycle, making it easy to ignore. Sanitation must be brought into the mainstream - out of the shadows, and onto the public agenda. Without such exposure, the issue will continue to be ignored by governments, aid agencies, local politicians and others, despite its importance to human development and economic growth.
I have seen the impact that a lack of access to such basic human rights as sanitation and water has on the world's poorest people. United Nations Secretary General Ban Ki-moon has convened the MDG Advocacy Group to accelerate progress in eradicating extreme poverty. As the world works to meet the MDG targets by 2015, we are committed to ensuring that those across the developing world are freed from the abject and dehumanizing conditions of extreme poverty as set out in the UN Millennium Declaration of 2000.
Only with an international approach that cuts across all the goals and involves governments, civil society groups, international organizations, the academic world and the private sector will we have a chance of meeting the goals.
With only five years remaining until the 2015 deadline, there is no more critical time to act. Heads of State convening at this historic meeting must work to keep their promises to the world's poorest people. We can no longer let sanitation be a silent issue. In order to live a life of dignity, the voices of the billions of people deprived of this basic human right need to be heard. The health of our world is at stake.