“Stool culture only” (i.e., a culture plate yielding microbial colonies without visible fecal particulates) is best termed a rectal swab–equivalent or fecal-sparse specimen and should be handled as a low-quality stool sample requiring enrichment or recollection. 1, 2
Rationale and terminology use
- Laboratories commonly treat such specimens like rectal swabs: low fecal biomass, adequate for some cultures but suboptimal for comprehensive pathogen detection; enrichment broths are recommended, and recollection of a true diarrheal stool (takes the shape of the container) is preferred for morbidity-relevant diagnoses 1, 2.
- IDSA defines the optimal specimen as a diarrheal stool; rectal swabs (or fecal-sparse “stool culture only” submissions) are acceptable but inferior and often require enrichment to avoid false negatives that could impact outcomes (missed STEC, Salmonella, Campylobacter, C. difficile) 1, 2.
Practical/algorithmic handling
- If only colonies/no stool seen: annotate as “rectal swab–equivalent/low-volume stool,” perform broth enrichment before toxin/PCR testing when applicable, and request recollection of a proper diarrheal stool to protect patient outcomes 2, 3.
- Pitfalls to avoid: direct toxin testing on such low-mass specimens without enrichment (reduced sensitivity) and overinterpreting negative results; prioritize recollection for high-stakes targets (e.g., STEC, C. difficile) affecting morbidity, mortality, and QOL 2, 1.