Michael Specter, in his article about the human microbiome, lists the reasons for the great leap in life expectancy that occurred in the United States and other developed countries during the twentieth century (“Germs Are Us,” October 22nd). This list includes the defeat of infectious diseases such as smallpox and polio, better nutrition, clean water, and “most important, perhaps, antibiotics.” In fact, in all likelihood the most important was clean water. The chlorination of urban water supplies starting in the early part of the last century eliminated waterborne infectious diseases such as typhoid fever, cholera, and dysentery, among others. This is why providing access to clean water and adequate waste-treatment infrastructure is critical to the future of people in developing countries.

Erica Schoenberger

Department of Geography and Environmental Engineering

Johns Hopkins University

Baltimore, Md.