What stool laboratory tests are indicated for a patient with persistent diarrhea following antibiotic treatment?

From the Guidelines

For a patient with persistent diarrhea after antibiotics, I recommend ordering a stool test for Clostridioides difficile (C. diff) as the primary diagnostic test, including both a C. diff toxin assay and PCR for toxin genes, as well as a comprehensive stool panel that includes stool culture for bacterial pathogens (Salmonella, Shigella, Campylobacter, E. coli O157:H7), ova and parasite examination, and fecal leukocytes or calprotectin to assess inflammation, as suggested by the 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea 1.

The guidelines recommend testing for C. difficile in people with a history of diarrhea following antimicrobial use and in people with healthcare-associated diarrhea 1. A single diarrheal stool specimen is recommended for detection of toxin or a toxigenic C. difficile strain (eg, nucleic acid amplification testing) 1.

Key tests to consider include:

• C. diff toxin assay
• PCR for toxin genes
• Stool culture for bacterial pathogens (Salmonella, Shigella, Campylobacter, E. coli O157:H7)
• Ova and parasite examination
• Fecal leukocytes or calprotectin to assess inflammation
• Consider testing for norovirus and rotavirus, especially if there's a community outbreak
• Fecal occult blood testing to evaluate for mucosal damage

It is crucial to collect stool samples before starting any new antibiotics or anti-diarrheal medications to avoid false-negative results. Antibiotic-associated diarrhea occurs in 5-30% of patients taking antibiotics, with C. difficile being the most serious cause in about 10-20% of these cases 1. C. diff infection specifically can lead to pseudomembranous colitis and potentially life-threatening complications if not promptly diagnosed and treated.

From the Research

Stool Labs for Diarrhea after Antibiotics Treatment

To diagnose the cause of persistent diarrhea after antibiotics treatment, the following stool labs can be ordered:

• Stool toxin test to detect the presence of Clostridioides difficile toxins 2, 3, 4
• Polymerase chain reaction (PCR) test to detect the presence of Clostridioides difficile DNA 3
• Stool culture to detect the presence of Clostridioides difficile bacteria 4

Key Considerations

When ordering stool labs, consider the following:

• The patient's symptoms and medical history, including recent antibiotics use 2, 3, 4
• The potential for false-negative results, especially if the patient has recently taken antibiotics 4
• The need for repeat testing if the initial results are negative but symptoms persist 4

Treatment Options

Based on the stool lab results, treatment options may include:

• Fidaxomicin or vancomycin for Clostridioides difficile infection 2, 3, 5
• Fecal microbiota transplantation (FMT) for recurrent Clostridioides difficile infection 3, 5
• Alternative treatment approaches, such as bacteriophages, probiotics, or monoclonal antibodies 6