An illness in humans caused by Campylobacter jejuni or C. coli. Campylobacteriosis ranges from a mild illness with diarrhea lasting a day, to severe abdominal pain, and severe diarrhea (sometimes bloody), sometimes accompanied by fever, occasionally lasting for several weeks. The incubation period for most cases is 2 to 5 days, and the illness usually lasts from 2 to 10 days, depending on its severity. Although the illness is generally regarded as a relatively mild disease, death can occur in some cases, especially for the very young, very old, or immunocompromised. A small percentage of cases develop Guillain-Barré Syndrome.