Now the fear has struck again: Researchers at Quinnipiac University analyzed toothbrushes belonging to students who shared a bathroom with an average of nine people. They found that 60 percent of the brushes had fecal coliform bacteria on them, and there was an 80 percent chance that the bacteria came from someone else. This means your roommate's microscopic poop particles could be on your toothbrush. I repeat, your roommate's microscopic poop particles could be on your toothbrush. (There are, thankfully, two caveats: The study was presented at the annual meeting of the American Society for Microbiology, so the findings should be considered preliminary until published in a peer-reviewed journal, and it wasn't reported how many toothbrushes were analyzed.)
As Science of Us reported in the wake of the Poop Beard Crisis, there's fecal bacteria (not actual feces) on our bodies and on most surfaces, but it probably won't make you sick. Coliform bacteria lives in our intestines and it's likely not harmful on its own, though it could suggest the presence of disease-causing germs like E. coli. But hey, this gives you another reason to whine about your roommate's bathroom habits.