Bacteria of what are now regarded as the genus Campylobacter were first isolated in 1909, but initially were considered as pathogens of animals only. Although the first human infections were reported in 1947, the importance of campylobacters as causes of intestinal illnesses was not widely recognized until the 1970s. C. jejuni and closely related species are now known as leading causes of bacterial gastroenteritis. C. fetus causes systemic diseases, primarily in compromised hosts. Most recently, C. pylori has been associated with antral gastritis and peptic ulcer disease. The pathogenic mechanisms for these three related organisms, while still being elucidated, are now known to be substantially different.