One of the unreported medical problems during the 1991 Gulf War was the extent to which troops got diarrhea. At least 57 percent of army troops had at least one bout of it and 20 percent had it so bad that they were out of action for a few days. This is an old problem, even tourists experience it when they visit country that has enough diarrhea causing bacteria present. The Persian Gulf is actually awash in all sorts of hostile bacteria, some of it fatal, and some of it generally unknown to Western medical experts. Since the Gulf War, the U.S. Army has been working on a vaccine for the most common diarrhea causing bacteria and currently has four vaccines being tested. Such a vaccine will not only help the troops, but also the natives of the, largely tropical, "diarrhea zone." While the locals build up some resistance to the bacteria, they still get diarrhea from time to time. The diarrhea can kill infants and people already weak from other illnesses.