Campylobacter

If you've had cramping and diarrhea, especially with blood or fever, stool testing can help identify Campylobacter as the cause. A positive result supports that diagnosis when the symptoms fit, but detecting bacterial DNA alone doesn't establish why you're ill or whether you need an antibiotic.

Common sources include undercooked poultry, unpasteurized milk, untreated water, and contact with infected animals. Most illnesses resolve within about a week. Older adults and people with weakened immune systems have a greater risk of severe infection.

What the Test Picks Up

Campylobacter includes several species with different effects on health. C. jejuni causes most recognized human infections, followed by C. coli. These bacteria can inflame the intestine and cause watery or bloody diarrhea.

This stool PCR detects genetic material from intestinal Campylobacter species, including C. jejuni and C. coli. PCR copies selected stretches of bacterial DNA until they can be detected. The clinically useful result is whether that DNA is present in the sample. It doesn't measure the severity of intestinal injury or show whether the bacteria are alive.

Stool PCR is an established diagnostic method for suspected intestinal infection. Using a Campylobacter result to predict future inflammatory disease or assess the health of an otherwise symptom-free gut has not been validated.

How PCR, Culture, and Antigen Tests Compare

Culture attempts to grow living bacteria from stool. Campylobacter needs particular growth conditions and can lose viability during transport, so culture can miss infections. Antigen tests detect bacterial proteins. Their performance varies substantially between products and study populations.

These studies explain why the methods can disagree. The accuracy figures describe the particular assays and comparisons studied. Culture remains useful because recovering live bacteria allows antibiotic susceptibility testing and helps public health teams investigate outbreaks.

Bloody Diarrhea and Gut Inflammation

Campylobacter infection commonly causes cramps, fever, and watery or bloody diarrhea. In a study of young children in Peru, the odds of detecting C. jejuni or C. coli were about 15 times higher in children with bloody diarrhea than in children without diarrhea. Other Campylobacter species did not show the same association with bloody diarrhea.

Inflammation markers in stool can rise during infection, but they don't identify the organism responsible. Similar symptoms can occur with Shigella, Salmonella, Shiga toxin-producing E. coli, and noninfectious bowel conditions.

Spread Into the Bloodstream

Campylobacter occasionally causes bloodstream infection. A Swedish study compared people with positive blood cultures against people with intestinal infection and negative blood cultures. Those with bloodstream infection were older and more likely to develop sepsis. Sepsis is a dangerous response to infection that can damage organs.

A meta-analysis of 29 studies involving 2,066 people with confirmed bloodstream infection estimated mortality at about 7%. That figure describes people whose infection had already reached the blood; it is not the risk attached to a positive stool result.

C. fetus is particularly associated with infections of blood vessels and heart valves. A French study selected 57 people who already had these complications, and about a quarter died. In a separate bloodstream-infection study, cancer was associated with about fivefold higher odds of death among people with C. fetus. These findings concern invasive disease diagnosed through blood or tissue specimens and cannot be inferred from stool PCR.

Low Antibody Levels and Persistent Infection

Antibodies help the immune system recognize and fight infections. Hypogammaglobulinemia means you have abnormally low amounts of these proteins. People with severe antibody deficiencies can develop prolonged or recurrent Campylobacter infections, sometimes lasting years.

A prospective study of 73 adults receiving antibody replacement documented C. jejuni and C. coli in stool using PCR and culture. Its positive-sample group also had higher stool calprotectin, although that group included a related organism outside the Campylobacter genus. The study shows that infection can occur during antibody replacement; it does not show that replacement therapy is ineffective.

Symptoms That Outlast the Infection

Some people develop irritable bowel syndrome after Campylobacter infection. Estimates depend heavily on how symptoms are counted. An English study of medical records found recorded complications in fewer than 2% of 20,471 people with Campylobacter or Salmonella infection combined. That figure covered diagnoses entered into health records, which can miss persistent symptoms.

A Minnesota study actively surveyed people after culture-confirmed Campylobacter infection. Among respondents without previous irritable bowel syndrome, 21% met symptom criteria for it six to nine months later. Fewer than half of those invited responded, so selection could affect that estimate. The two studies measured different outcomes in different ways.

People with lasting bowel symptoms have also shown reduced diversity of gut bacteria and slower recovery of that bacterial community. This is an association, and a commercial microbiome profile has not been shown to identify the cause of an individual's post-infection symptoms.

Other recognized complications include reactive arthritis and, rarely, Guillain-Barré syndrome. Reactive arthritis causes joint inflammation after an infection. Guillain-Barré syndrome occurs when the immune system damages nerves, causing tingling and weakness that often begin in the legs.

Microscopic Colitis and the Species Question

Research on C. concisus concerns a different species from the usual food-poisoning organisms. It commonly inhabits the mouth and is outside the usual targets of intestinal Campylobacter PCR. Findings about it cannot be assigned to a routine positive C. jejuni/C. coli result.

A Danish study linked stool cultures positive for C. concisus to later microscopic colitis. This condition causes chronic watery diarrhea and requires colon biopsies for diagnosis. The rate of diagnosis was about 32 times higher than in matched population controls, falling to about nine times higher after the first year was excluded.

The association was weaker for C. jejuni and was no longer statistically conclusive after excluding the first year. People with negative stool cultures also had an increased rate of microscopic colitis. That pattern leaves room for pre-existing illness and the investigation of persistent diarrhea to explain part of the association.

Studies have also associated C. concisus and C. showae with inflammatory bowel disease. One study detected a broad range of Campylobacter DNA more often in colon biopsies from people with ulcerative colitis than in controls. These were tissue measurements involving different species, and they don't establish that Campylobacter caused the disease or that this stool result predicts it.

Heart and Kidney Findings After a Mixed Outbreak

After drinking water in Walkerton, Canada, was contaminated with both E. coli O157:H7 and Campylobacter, researchers followed 1,977 adults for eight years. Those who had acute gastroenteritis had a higher rate of new hypertension and about twice the rate of self-reported cardiovascular disease.

The roughly threefold increase reported for kidney impairment applied to having both reduced filtration and increased urine protein. The association with either finding alone was not statistically conclusive. Because exposure involved two organisms, including kidney-damaging E. coli O157:H7, this study cannot establish a Campylobacter-specific long-term risk or justify a monitoring schedule from a stool result alone.

Infants in Settings With Frequent Exposure

Research in communities with frequent exposure to contaminated food, water, and animal feces often detects Campylobacter in infants without diarrhea. These studies sometimes use broader tests that detect more Campylobacter species than routine intestinal pathogen PCR.

In a study of 1,715 children across eight resource-limited settings, repeatedly positive stool tests were associated with slower growth in length. The study could not reliably separate persistent infection from repeated new infections, and it did not prove that treating symptom-free detections improves growth. Its findings don't establish the benefit of routine screening in healthy children elsewhere.

Antibiotic Resistance

Resistance varies by species and location. In one Ethiopian study, a third of 30 C. jejuni/C. coli isolates from children resisted ciprofloxacin. A separate Burkina Faso study reported resistance in about three quarters of 33 isolates drawn from several Campylobacter species, and all resisted erythromycin.

Those small regional studies don't predict whether your strain is resistant. Stool PCR identifies bacterial DNA; susceptibility testing examines whether living bacteria grow in the presence of particular antibiotics.

When Results Can Be Misleading

• Detection after recovery: PCR can detect DNA from dead bacteria, but living bacteria can also remain in stool for weeks after symptoms improve. A persistent positive result cannot distinguish those possibilities.
• Detection without illness: Campylobacter DNA can occur in people without symptoms. Its presence alone does not establish a condition requiring treatment.
• Other species: A result for common intestinal Campylobacter targets does not describe every member of the genus, including mouth-associated species studied in chronic inflammatory conditions.
• Several possible causes: More than one intestinal pathogen can be present. Medication effects and noninfectious bowel disease can also contribute to diarrhea.
• Collection and laboratory interference: Improper handling, too little bacterial DNA, or substances that interfere with PCR can cause a negative or invalid result despite infection. Contamination can produce a false-positive result.
• Recent antibiotics: Treatment can reduce bacterial detection, while residual DNA may remain detectable. The result needs to be interpreted with the timing of symptoms and treatment.
• Severity and future risk: A positive stool result does not measure intestinal damage, diagnose bloodstream infection, or predict which person will develop a later complication.