Most Campylobacter species can cause disease and can infect humans and other animals. The bacterium's main reservoir is poultry; humans can contract the disease from eating food contaminated with Campylobacter species. Another source of infection is contact with infected animals, which often carry Campylobacter asymptomatically. At least a dozen species of Campylobacter have been implicated in human disease, with C. jejuni and C. coli being the most common. C. jejuni is now recognized as one of the main causes of bacterial foodborne disease in many developed countries. C. jejuni infection can also spread to the blood in individuals with AIDS, while C. lari is a known cause of recurrent diarrhea in children. C. fetus is a cause of spontaneous abortions in cattle and sheep, as well as an opportunistic pathogen in humans. This genus has been found to be part of the salivary microbiome.

Campylobacter can cause a gastrointestinal infection called campylobacteriosis. The incubation period is 24–72 hours after infection. This is characterized by inflammatory, sometimes bloody diarrhea or dysentery syndrome, mostly including cramps, fever, and pain. The most common routes of transmission are fecal-oral, ingestion of contaminated food or water, and the eating of raw meat. Foods implicated in campylobacteriosis include raw or under-cooked poultry, raw dairy products, and contaminated produce. Campylobacter is sensitive to the stomach's normal production of hydrochloric acid: as a result, the infectious dose is relatively high, and the bacteria rarely cause illness when a person is exposed to less than 10,000 organisms. Nevertheless, people taking antacid medication (e. g. people with gastritis or stomach ulcers) are at higher risk of contracting disease from a smaller amount of organisms, since this type of medication inhibits normal gastric acid. The infection is usually self-limiting and, in most cases, symptomatic treatment by liquid and electrolyte replacement is enough in human infections. Symptoms typically last five to seven days. Treatment with antibiotics has little effect and is discouraged except in high-risk patients. The sites of tissue injury include the jejunum, the ileum, and the colon. Most strains of C jejuni produce a toxin (cytolethal distending toxin) that hinders the cells from dividing and activating the immune system. This helps the bacteria to evade the immune system and survive for a limited time in the cells. A cholera-like enterotoxin was once thought to be also made, but this appears not to be the case. The organism produces diffuse, bloody, edematous, and exudative enteritis. Although rarely has the infection been considered a cause of hemolytic uremic syndrome and thrombotic thrombocytopenic purpura, no unequivocal case reports exist. In some cases, a Campylobacter infection can be the underlying cause of Guillain–Barré syndrome. Gastrointestinal perforation is a rare complication of ileal infection.

• PMID 15845230

• CDC