>Do you know where the next plague will come from? Neither do I, but the smart money might be on the sewage treatment plant around the corner from your house. The medical establishment has known for a while that the over prescribing of common antibiotics has created a series of newly resistant bacteria. I submit that the sludge slithering under your street may be a bigger problem in the long run.
Very few antibiotics are fully metabolized. You excrete some amount whenever you use the toilet. When you are sick, you excrete some of the bacteria as well. Plus, there are many types of moderately harmful bacteria that exist in even the cleanest bathrooms such as Staphylococcus, Streptococcus, E-coli, Salmonella and Campylobactor. All this is floating around in raw sewage, which is a fantastically rich growth medium.
So what you have here is a large, open air petri dish. Bacteria are free to grow, divide and mutate at will. Combine multiple strains of bacteria competing within this medium and you have a little evolutionary microcosm, with weaker strains dying and the stronger flourishing. Just wait until one of the winners hitches a ride out of the plant and makes its way to the general population.
Is the risk small? Certainly. Is it zero? You wish.