A majority of cases are mild and do not require hospitalization or treatment with antibiotics. However, C. jejuni infection can be severe. Children under the age of five and young adults aged 15 - 29 are the age groups most frequently affected. The incubation period is typically two to five days, but onset times of up to 11 days have been reported. Confirmation of C. jejuni as the cause of foodborne illness depends on being able to isolate the same strain of the organism from the suspect food and from patient stools.
Raw chicken is thought to be a major source of foodborne illness.
Cross-contamination of foods with raw chicken has been a factor in many of the reported outbreaks. Commercially processed foods are rarely a source of C. jejuni infection. This is because the organism is easily destroyed by most food processing treatments. Also, the organism grows poorly in foods and in the food processing environment. The poultry slaughtering and processing industry and government agencies are investigating ways of reducing or eliminating contamination.