There's a flip side to this story. While it's true that rates of certain acute diseases have gone down since NYC has gotten cleaner, rates of chronic diseases such as asthma have gone up. There's a school of thought that thinks our modern city existence is too clean, and we're no longer exposed to "old friends" that keep asthma and other chronic illnesses at bay. Check out the book "An Epidemic of Absence" for more details: http://amzn.to/12Blhij. In ten years from now, we may be taking pills for "beneficial parasites" as we do now for beneficial bacteria.