From the Guidelines
A stool culture is not always necessary when ordering separate stool bacterial testing, as molecular assays such as nucleic acid amplification tests (NAAT) can detect bacterial pathogens without the need for culture 1.
When to Consider Stool Culture
However, there are certain situations where stool culture is still recommended:
- When antimicrobial susceptibility testing is required, as culture is necessary to determine the susceptibility of the isolated organism to different antibiotics 1.
- In cases of suspected outbreaks, where culture can help identify the specific strain of the pathogen and facilitate public health investigations 1.
- When a specific bacterial pathogen is suspected, such as Salmonella, Shigella, or Campylobacter, and the laboratory has the capability to perform specialized cultures or molecular assays 1.
Molecular Assays
Molecular assays, such as NAAT, are increasingly being used for the diagnosis of infectious diarrhea, as they offer high sensitivity and specificity, and can detect a wide range of bacterial, viral, and parasitic pathogens 1.
Specimen Collection
It is essential to collect a diarrheal stool specimen, rather than a rectal swab, as it provides greater fecal material and is less prone to environmental degradation, increasing the likelihood of detecting infectious agents 1.
Clinical Judgment
Ultimately, the decision to order a stool culture or molecular assay should be based on clinical judgment, taking into account the patient's symptoms, medical history, and epidemiological risk factors, as well as the availability of laboratory resources and expertise 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.
- Stool culture is considered the gold standard method for diagnosing enteric bacterial infections, but it has a low yield of detecting an underlying pathogen in some cases 2.
- A study found that only 4% of stool cultures performed on patients with acute gastroenteritis yielded growth of pathogenic bacteria, suggesting that stool culture may not be necessary for all patients with this condition 2.
Alternative Testing Methods
- Molecular platforms, such as the BD MAX Enteric Bacterial Panel (EBP), offer a rapid and efficient alternative to conventional stool culture, with results available in a significantly shorter timeframe 4.
- Metagenomics-based stool testing approaches, such as shotgun metagenomics, can provide diagnostic and public health information, and may be more accurate and affordable than traditional stool culture methods 5.
- PCR panels can also be used to detect enteric bacterial pathogens in stool, and may be more rapid and accurate than stool culture in some cases 5, 6.
Clinical Predictors of Positive Stool Culture
- Certain clinical predictors, such as fever, duration of abdominal pain, and requirement of IV fluid therapy, may be associated with a positive stool culture 3.
- However, other factors, such as bloody diarrhea or persistent diarrhea, may not be associated with a positive stool culture 3.
- The decision to order a stool culture should be based on a careful evaluation of the patient's clinical presentation and medical history, rather than relying solely on laboratory testing 6, 2.