What is the likely cause of a patient's dark, possibly blood-tinged diarrhea, with Bristol stool chart types 4-6, who tested positive for Campylobacter on Gastro PCR (Gastrointestinal Polymerase Chain Reaction) and had a normal Complete Blood Count (CBC), with no significant underlying medical conditions?

Campylobacter Infection is the Likely Cause

The most likely cause of this patient's diarrhea is Campylobacter infection, as confirmed by the positive Gastro PCR result. The clinical presentation—including the variable stool consistency (Bristol types 4-6), bright yellow coloration, dark edges suggesting possible blood, and the positive Campylobacter detection—is entirely consistent with this diagnosis 1, 2.

Understanding the Clinical Picture

Campylobacter jejuni/coli causes acute gastroenteritis with a highly variable clinical presentation, ranging from watery diarrhea to bloody, mucoid stools 1, 3. The key features in this case align with typical Campylobacter infection:

• Variable stool patterns (Bristol 4-6) are characteristic of Campylobacter enteritis, which can present as watery, mucoid, or bloody diarrhea 1, 4
• The bright yellow color likely represents rapid intestinal transit and bile pigment, common in acute infectious diarrhea 1
• Dark coloration at edges suggests occult blood, which is frequently present in Campylobacter infection even when not grossly bloody 2, 4
• The normal CBC indicates the patient is not severely ill and has no significant systemic complications at this point 2

Why Campylobacter Fits Perfectly

Campylobacter is one of the most common causes of acute bacterial gastroenteritis worldwide and is the leading bacterial cause in developed countries 3, 5. The infection typically presents with:

• Incubation period of 2-5 days before symptom onset 4
• Fever, abdominal pain, and diarrhea that can be watery or bloody 1, 4
• Self-limiting course in most immunocompetent patients 3, 4
• The small intestine and colon are both involved, making it more accurately described as enterocolitis rather than simple enteritis 4

Important Clinical Considerations

Abdominal pain can be particularly severe with Campylobacter and may even mimic appendicitis, especially in younger patients 1. This is a common pitfall—don't rush to surgical evaluation without considering infectious causes when stool testing is positive 1.

The normal CBC is reassuring but doesn't rule out the need for monitoring. While most Campylobacter infections are self-limited, complications can occur including 1:

• Guillain-Barré syndrome (the most concerning late complication, occurring in a small percentage of cases) 1, 3
• Reactive arthritis (can develop weeks after infection) 1
• Bacteremia (rare, but more common in immunocompromised patients) 1

Treatment Approach

For immunocompetent patients with non-severe Campylobacter infection, supportive care alone is often sufficient 1, 6. However, specific situations warrant antimicrobial therapy:

When to Treat with Antibiotics:

• Severe intestinal infection (high fever, bloody diarrhea, severe abdominal pain) 1, 3
• Immunocompromised patients 1
• Signs of systemic illness or bacteremia 1, 2
• Symptoms persisting beyond 7 days 1

Antibiotic Selection:

Azithromycin is now the preferred first-line agent due to increasing fluoroquinolone resistance in Campylobacter 1, 2, 5:

• Azithromycin 500 mg on day 1, then 250 mg daily for 4 days 2
• Alternative: Ciprofloxacin 500 mg twice daily for 3-5 days (only if local resistance rates are low) 2
• Erythromycin is also effective and commonly used 4

Critical caveat: The increasing prevalence of quinolone resistance (approaching 50% in some regions) makes azithromycin the safer empiric choice 5.

Supportive Care is Essential

Regardless of antibiotic use, hydration and electrolyte management are the cornerstone of treatment 2, 6:

• Oral rehydration with low-osmolarity solutions should be initiated immediately 2
• Monitor for dehydration through skin turgor, mental status, mucous membranes, and vital signs 2
• Avoid antiperistaltic agents (like loperamide) in bloody or febrile diarrhea, as they may prolong infection 1

Monitoring and Follow-Up

Track clinical improvement over the next 3-7 days 2:

• Frequency and character of stools should gradually improve 2
• Temperature normalization typically occurs within 2-3 days of appropriate treatment 2
• Persistent symptoms beyond 14 days warrant re-evaluation for post-infectious IBS or other complications 1

Be aware that post-infectious IBS develops in 10-14% of patients following Campylobacter infection, with IBS-D (diarrhea-predominant) or IBS-M (mixed) being most common 1. This can persist for months to years after the acute infection resolves 1.

Source and Prevention

Campylobacter is primarily transmitted through contaminated poultry (the main reservoir), unpasteurized milk, or untreated water 3, 5. Person-to-person transmission is less common but possible 4. Source attribution analysis suggests most human infections come from poultry or generalist sources 5.