From the Guidelines
No, a stool culture is not always necessary when ordering separate stool bacterial testing, but it is required in certain situations, such as when a bacterial pathogen is detected by culture-independent diagnostic testing, including antigen-based molecular assays, to ensure that outbreaks of similar organisms are detected and investigated 1.
Key Considerations
- Stool testing should be performed for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and STEC in people with diarrhea accompanied by fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis 1.
- A stool culture is necessary when a bacterial pathogen is detected by culture-independent diagnostic testing to ensure that outbreaks of similar organisms are detected and investigated, and for antimicrobial susceptibility testing 1.
- NAAT (nucleic acid amplification test) is recommended for the detection of Clostridium difficile, Shiga toxin–producing Escherichia coli, and other bacterial pathogens 1.
Specific Situations
- In cases of uncomplicated traveler’s diarrhea, diagnostic testing is not recommended unless treatment is indicated, but stool testing should be performed if symptoms persist for 14 days or longer 1.
- For immunocompromised individuals, a broader set of bacterial, viral, and parasitic agents should be considered, and stool culture may be necessary to detect certain pathogens 1.
From the Research
Necessity of Stool Culture
- The necessity of stool culture when ordering separate stool bacterial testing is debatable, with some studies suggesting that it may not be necessary in all cases 2, 3.
- A study published in 2022 found that metagenomics-based stool testing approach could simultaneously provide diagnostic and public health information, and may be more routinely applied in clinical and public health laboratories as cost, speed, and analytics improve 4.
- Another study published in 2020 found that stool cultures had a very low yield of detecting an underlying pathogen in patients with acute gastroenteritis, and played little to no role in patient management for the vast majority of patients 2.
Predictors of Positive Stool Culture
- A study published in 2002 found that clinical predictors of positive stool culture in adult patients with acute infectious diarrhea included summer season, fever, duration of abdominal pain, and requirement of IV fluid therapy 5.
- However, another study published in 1988 found that bacterial stool culture and ova and parasite identification were not indicated for patients with nosocomial diarrhea, and that elimination of these unnecessary stool tests would have saved the hospital approximately $7530 in the 18-month study period 3.
Comparison of Stool Culture Methods
- A study published in 2015 compared the time-motion analysis of conventional stool culture and the BD MAX™ Enteric Bacterial Panel (EBP), and found that the EBP resulted in significant time savings and a shorter time-to-result for patients with acute bacterial diarrhea 6.
- The study found that with conventional culture, negative culture results were available from 41:14:27 to 54:17:19, while with EBP, positive and negative results were available from 2:28:40 to 3:33:39 6.