Campylobacter jejuni is a bacterium and one of the most common causes of food poisoning worldwide. It takes remarkably few organisms to make you sick: as few as 500 to 800 bacteria can trigger an infection, which is far less than most other foodborne pathogens. In the United States, the reported incidence is roughly 14 per 100,000 people annually, though actual cases are believed to be much higher since many go unreported.
How C. Jejuni Causes Illness
C. jejuni is a spiral-shaped, Gram-negative bacterium that thrives in low-oxygen environments, a trait called microaerophily. It colonizes the intestinal lining of birds and many other animals without making them sick, but in the human gut it behaves very differently. Once ingested, the bacteria invade the cells lining your intestines and produce a toxin called cytolethal distending toxin (CDT).
This toxin works by getting absorbed into your intestinal cells and traveling backward through the cell’s internal transport system until it reaches the nucleus, where your DNA is stored. Once there, it acts like an enzyme that cuts DNA strands apart. The damaged DNA triggers the cell to halt its normal cycle of growth and division, causing the cell to swell and eventually die. This widespread cell damage is what drives the cramping, inflammation, and bloody diarrhea that characterize the infection.
Where the Bacteria Come From
Poultry is the single biggest source. C. jejuni lives harmlessly in the guts of chickens and can contaminate meat during processing. Eating undercooked chicken or letting its juices contact other foods in your kitchen is the most common way people get infected.
Raw (unpasteurized) milk is another well-documented source. The bacterium is ubiquitous in dairy environments, and contamination can come from fecal matter, wild bird droppings, poorly sanitized milking equipment, or even silent udder infections in cows. During a 2014 outbreak in Utah, over half of patients who hadn’t directly consumed raw milk had eaten queso fresco, a fresh cheese made from it. Untreated drinking water and contact with pet dogs or cats can also transmit the bacteria, though less frequently.
Symptoms and Timeline
Symptoms typically appear 2 to 5 days after exposure, though the window can stretch from 1 to 10 days. The illness usually lasts 3 to 6 days and includes:
- Diarrhea, frequently bloody
- Abdominal cramping and pain
- Fever
- Nausea and vomiting
- Headache
Most healthy adults recover on their own without specific treatment. The biggest immediate risk is dehydration from fluid loss, especially in young children and older adults. Replacing fluids and electrolytes is the most important step during recovery.
Guillain-Barré Syndrome and Other Complications
The most serious complication of C. jejuni infection is Guillain-Barré syndrome (GBS), a condition where the immune system attacks the nerves outside the brain and spinal cord, causing weakness in the limbs and loss of reflexes. C. jejuni is the single most frequent infection to precede GBS.
The connection comes down to a case of mistaken identity at the molecular level. The outer coating of certain C. jejuni strains carries structures that closely resemble gangliosides, which are molecules found on the surface of human nerve cells. When the immune system builds antibodies to fight off the bacterial infection, those same antibodies can mistakenly target nerve tissue. GBS following C. jejuni tends to be a severe, purely motor form, meaning it primarily affects movement rather than sensation. While GBS is rare overall, it can lead to temporary paralysis and months of rehabilitation.
Reactive arthritis, which causes joint pain and swelling weeks after the initial infection, is another possible complication. It typically resolves over time but can persist for months.
How the Infection Is Diagnosed
Doctors diagnose campylobacteriosis through stool testing. Traditional stool cultures grow the bacteria on special plates under low-oxygen conditions, but this method is slow and misses some cases. PCR-based tests, which detect the bacterium’s DNA directly, are faster and more sensitive. In controlled studies, PCR caught about 96% of confirmed positive samples compared to roughly 80 to 87% for culture. Many labs now use PCR as a first-line screening tool, with culture reserved for cases where antibiotic resistance testing is needed.
Treatment and Antibiotic Resistance
Most people recover without antibiotics. Treatment is reserved for severe illness or for people at higher risk of complications, such as those with weakened immune systems, very young children, and older adults.
When antibiotics are necessary, azithromycin is the preferred choice. Fluoroquinolones like ciprofloxacin are an alternative, but resistance to this drug class has been climbing steadily. Among C. jejuni samples from U.S. patients, ciprofloxacin resistance rose from 17% in the late 1990s to 27% by 2015 to 2017, with 28% of isolates resistant in 2017. Azithromycin resistance remains much lower, at about 3% for C. jejuni, which is why it’s now favored as the go-to option.
Preventing Infection
Cooking poultry to the right temperature is the single most effective step. The USDA recommends an internal temperature of 165°F (73.9°C) for all poultry products. Research shows that C. jejuni is killed at 158°F (70°C) when held for at least 2 minutes, so hitting the USDA target provides a comfortable safety margin. Use a meat thermometer, especially with thicker cuts and chicken livers, which have been linked to multiple restaurant outbreaks when served pink inside.
Cross-contamination in the kitchen is the other major risk. Use separate cutting boards for raw poultry and ready-to-eat foods. Wash your hands, utensils, and surfaces with hot soapy water after they contact raw chicken or its juices. Avoid rinsing raw chicken in the sink, which can splash bacteria onto surrounding surfaces. Drink only pasteurized milk and treated water, and wash hands thoroughly after handling pets or farm animals.