I am surprised to see your posting, because the health externality of hygiene and sanitation is the main focus of my coauthored paper that you and I discussed both in New Delhi and DC. As you know the paper is currently under review and it has been in circulation, in its earliest drafts. In fact the paper is also available on the World Bank website since 2008. I hope you will revise your piece to give the due credit. In fact the title of your blog post is directly from my paper.