Why not prescribe antibiotics more widely? First, there’s the issue of antibiotic-resistant strains developing, though this is less of a concern with some of the newer regimens that wipe out infections in a single day—likely not enough time for a resistant strain to evolve and thrive. More worrisome, perhaps, is recent research showing that the colons of overseas travelers who treat their diarrhea with antibiotics, particularly in Southeast Asia, tend to become colonized with two species of “bad” bacteria that they then carry home and can spread around town. Both bugs may inhabit a traveler’s gut only briefly and cause no problems while they’re there, but they are dangerous to patients with weak immune systems. Here again, with the newer single-dose regimens, it may not be an issue.