World War I soldiers still suffered from disease in staggering rates, but avoiding disease became a much greater priority for all of the armies involved than ever before. Western army camps emphasized sanitation, building better ditches and other facilities to divert sewage from water supplies. American soldiers, by far the healthiest in the war, also received typhoid fever inoculations. There were major improvements on both sides in using sanitary procedures in army hospitals, which led to much lower (but still frightfully high) rates of infection, including tetanus, in wounded soldiers than in previous conflicts. Ambulances were also motorized, which meant that soldiers could be removed from the front more quickly. For all the many advances, however, disease remained a major problem for the armies, especially in Europe. The horrific influenza outbreak that killed millions worldwide in 1918-1919 began in the trenches of World War I.