Like some other forms of gram-negative sepsis, septicemic plague can cause disseminated intravascular coagulation, and is almost always fatal when untreated (the mortality rate in medieval times was 99-100 percent). However, it only occurs in a minority of cases of Yersinia infection, so that fewer than 5,000 people a year acquire the disease. It is in fact the rarest of the three plague varieties; the other forms are bubonic and pneumonic plague.[1]