Campylobacter is a genus of bacteria that is among the most common causes of bacterial diarrheal illness in humans worldwide. It is a gram-negative rod-shaped bacterium that grows best in a high temperature (42°C, or 107°F) and low oxygen environment.

Campylobacter infection is commonly associated with the consumption of raw (unpasteurized) milk, undercooked poultry, and contaminated water; however, most Campylobacter cases are sporadic and are never traced back to a specific food or beverage. Nonetheless, very large outbreaks (greater than 1,000 illnesses) have been documented, most often from consumption of contaminated milk or unchlorinated water supplies. Not all Campylobacter infections cause obvious illness. Symptomatic infection occurs almost exclusively in infants and young children, who can be infected repeatedly. The amount of time from infection to symptom onset—typically referred to as the incubation period—can vary to a significant degree.  It is relatively short, ranging from 1 to 7 days, with an average of 3 days. 

Although uncommon, Campylobacter infection can lead to disorders of the nervous system such as Guillain-Barré syndrome (GBS), as well as reactive arthritis, irritable bowel syndrome, and other functional gastrointestinal disorders (i.e., indigestion, constipation, and acid reflux).