I have always believed that the most significant medical discovery of the past century or so was penicillin. Perhaps I think that way since penicillin was a part of my childhood, prone to bronchitis and pneumonia as I was. But according to a poll by the British Medical Journal, the most important medical breakthrough of the last 167 years is (i.e. the entire existence of the BMJ): Sewers.
Fond as I am of the flushing toilet and a well-functioning drain in my sink, and in spite of touring a water-cleansing plant here in Bergen, I did not think of sewers. I may instead have thought of hand-washing or of aspirin.
More than 11,000 readers responded, and sanitation won with 1,795 votes. London was one of the first modern cities to improve public sanitation after John Snow showed that cholera was spread by water, and Edwin Chadwick came up with the idea of sewage disposal and piping water into homes. (From the Washington Post)
Bergen was one of the first cities in Norway to get indoor plumbing but not because of John Snow's proof of cholera's connection to sewage (made in 1853 after yet another cholera outbreak). Bergen's priority in 1855 for making a serious effort to get regular running water to the people were fires and dry wells. But an appropriate handling of waste was far rarer, even after Bergen's devastating cholera epidemic in 1868. Gutters were a matter of road-building, not water-handling. A true sewer system did not come about until after 1910, when the flushable toilet was introduced and with it, huge pollution of the bay. By 1928, pumps were installed at key points in the downtown area to direct the sewage, and those pumps are still in use today.
How did the rest of the voting go?
Antibiotics was a close second with 1,642 votes. Anesthesia came in third with 1,574 votes, followed by vaccines and the discovery of the structure of DNA. (ibid)