Stool culture

When to request this test

Stool culture is used to identify bacterial pathogens responsible for acute diarrhea, whether acqueous (choleriform syndrome) or with mucus and blood (dysenteric syndrome).

A stool culture should not be requested in a patient who doesn’t have diarrhea.

This examination is used to detect the bacteria most frequently responsible for infectious diarrhoea, namely:

• Salmonella spp
• Shigella spp
• Campylobacter spp
• Yersinia spp

Stool testing should be performed for Salmonella, Shigella, Campylobacter, Yersinia in people with diarrhea accompanied by fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis.

Other pathogens, including viruses, are only tested in special circumstances.

The indications for stool culture are therefore the following situations:

• Acute febrile diarrhea
• Febrile collective food poisoning
• Diarrhea with signs of clinical severity
• Acute or chronic diarrhea in immunocompromised patients (Acute diarrhea is defined by ≥ 3 liquid and/or loose (not molded) stools per day for < 14 days)

There is no indication to perform a stool in the following situations:

• Immunocompetent subjects with acute diarrhea (without mucus, blood, choleriform syndrome or fever)
• Moldy stools
• In patients hospitalized for ≥3 days with acute diarrhea if they do not consume outside food

As with all bacteriological tests, this examination should ideally be done before starting any antibiotic therapy.

Follow-up testing is not recommended in most people for case management following resolution of diarrhea. A clinical and laboratory revaluation may be indicated in people who do not respond to an initial course of therapy, and should include consideration of non-infectious conditions.

Interferences & limitations

• The use of antibiotics or antidiarrheal drugs can inhibit the growth of pathogenic bacteria, leading to false-negative results. It is recommended to stop antibiotics before sample collection, if possible.
• Co-infections: the presence of multiple pathogens in the stool can complicate result interpretation, as some microorganisms may interfere with others.
• Hard-to-culture pathogens: some pathogenic microorganisms (e.g., Campylobacter, Vibrio), may not be detected if the culture media or methods used are not appropriate.