From the Guidelines
Stool PCR is significantly more sensitive than stool culture for ruling out infectious gastroenteritis, with sensitivity rates of 94-98% compared to 60-70% for traditional stool cultures. The main advantage of PCR testing is its ability to directly detect the genetic material of pathogens, allowing it to identify organisms that may be present in small quantities or those that are difficult to grow in laboratory conditions, as noted in the 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea 1.
Key Differences Between Stool Culture and PCR
- Stool cultures require viable organisms that can grow on specific media, which limits their effectiveness when patients have already started antibiotics or when dealing with fastidious organisms.
- PCR provides faster results, typically within hours, versus 2-3 days for cultures, and can simultaneously test for multiple pathogens in a single sample.
- However, PCR cannot determine antibiotic susceptibility and may detect non-viable organisms or residual DNA that aren't causing current symptoms.
Recommendations for Diagnostic Testing
- For comprehensive evaluation, PCR is preferred as the initial test due to its superior sensitivity.
- Culture may still be needed for antibiotic susceptibility testing in certain cases, as recommended by the guidelines 1.
- It's essential to consider the specific pathogens being tested for, as some may require specialized cultures or molecular assays, and to consult with the laboratory for instructions regarding container, temperature, and transport guidelines to optimize results.
From the Research
Comparison of Stool Culture and Stool PCR for Diagnosing Infectious Gastroenteritis
- Stool culture is the traditional method for diagnosing bacterial intestinal infections, but it has a low sensitivity and requires more than 24 hours to produce results 2.
- Stool PCR, on the other hand, is a molecular-based method that can detect multiple pathogens simultaneously and has been shown to be more sensitive than traditional stool culture 3.
- A study comparing traditional microbiology with a commercial syndromic molecular-based panel found that the molecular-based panel was more sensitive and had a faster turnaround time for some targets, particularly for viruses and protozoa 3.
- The use of PCR-based molecular diagnosis can identify etiological agents of acute diarrhea more accurately and quickly than conventional stool culture 2.
- However, it's worth noting that stool culture is still an important tool for diagnosing bacterial gastroenteritis, particularly for identifying and tracking outbreaks of bacterial gastroenteritis 4.
Sensitivity of Stool Culture vs. Stool PCR
- Stool culture has a low sensitivity, requiring more than 24 hours to produce results, and may not detect all types of bacteria, viruses, or protozoa 2.
- Stool PCR, on the other hand, has been shown to be more sensitive, particularly for detecting viruses and protozoa, and can produce results more quickly 3.
- A study found that the use of a commercial syndromic molecular-based panel increased the detection of rotavirus and adenovirus, and improved the positivity rates for certain bacteria and protozoa 3.
Clinical Implications
- The choice between stool culture and stool PCR may depend on the clinical presentation and the suspected etiological agent of the infectious gastroenteritis 5, 4.
- Stool PCR may be preferred for its speed and sensitivity, particularly for detecting viruses and protozoa, while stool culture may still be useful for identifying and tracking outbreaks of bacterial gastroenteritis 3, 4.