Indications for Stool and Blood Testing in Acute Diarrhea

Indications for Stool Testing

Order stool cultures for Salmonella, Shigella, Campylobacter, Yersinia, Clostridioides difficile, and Shiga‑toxin‑producing E. coli (STEC) when a patient presents with diarrhea accompanied by fever, bloody or mucoid stools, severe abdominal cramping/tenderness, or any sign of sepsis. [Infectious Diseases Society of America] 1
Add Vibrio species testing when the diarrhea is profuse “rice‑water” in consistency, the patient has recent exposure to salty or brackish water, has consumed raw/undercooked shellfish, or has traveled to cholera‑endemic regions within the prior 3 days. [Infectious Diseases Society of America] 1

Routine stool culture should detect Salmonella, Shigella, Campylobacter, and Yersinia enterocolitica (particularly in pediatric patients with right‑lower‑quadrant pain mimicking appendicitis or those with exposure to undercooked pork). [Infectious Diseases Society of America] 1
Test for Clostridioides difficile in patients older than 2 years who develop diarrhea after recent antimicrobial exposure. [Infectious Diseases Society of America] 2
Include STEC O157 detection using sorbitol‑MacConkey or chromogenic agar, and non‑O157 STEC detection via Shiga‑toxin assays or genomic tests. [Infectious Diseases Society of America] 1

Perform ova‑and‑parasite (O&P) examination (three specimens) when diarrhea persists for ≥14 days, when travel history suggests parasitic exposure, or when the patient is immunocompromised. [Infectious Diseases Society of America] 1
If O&P results are negative but symptoms persist, add a Giardia ELISA (≈92 % sensitivity, 98 % specificity). [Infectious Diseases Society of America] 3
In patients with advanced immunodeficiency, expand testing to include Cryptosporidium, Cyclospora, Cystoisospora, Microsporidia, Mycobacterium avium complex, and Cytomegalovirus. [Infectious Diseases Society of America] 1
Consider viral stool studies (norovirus, rotavirus, enteric adenovirus) during outbreak settings, in immunocompromised hosts, or when watery diarrhea lacks an identified bacterial pathogen. [Infectious Diseases Society of America] 4

Obtain blood cultures in infants younger than 3 months, in any age group with clinical signs of septicemia, in suspected enteric (typhoid) fever, in patients with systemic infection manifestations, in immunocompromised individuals, in those with hemolytic anemia, or after travel to enteric‑fever‑endemic regions with unexplained fever. [Infectious Diseases Society of America] 1
Do not routinely order blood cultures for isolated mucus‑containing diarrhea without fever or systemic signs. [Infectious Diseases Society of America] 3

When multiple cases arise in congregate settings (e.g., nursing homes, day‑care centers, shared meals), broaden testing to include bacterial, viral, and parasitic agents regardless of individual symptom severity. [Infectious Diseases Society of America] 1
Coordinate testing and case management with public‑health authorities. [Infectious Diseases Society of America] 1
Test affected individuals even if they lack fever or bloody stools. [Infectious Diseases Society of America] 1

Multiplex nucleic‑acid‑amplification panels detect DNA from both viable and non‑viable organisms; a positive result may represent colonization rather than active infection and therefore requires clinical correlation. [Infectious Diseases Society of America] 1

Order a comprehensive bacterial stool culture for Salmonella, Shigella, Campylobacter, Yersinia, and Shiga‑toxin‑producing E. coli when the patient presents with fever, bloody or mucoid stools, severe abdominal cramping, or any signs of sepsis. 5
Add Vibrio testing when the patient has consumed raw or undercooked shellfish, has recent exposure to brackish water, exhibits profuse “rice‑water” diarrhea, or has traveled to cholera‑endemic regions within the preceding three days. 5

Perform Clostridioides difficile testing first in any patient with recent antibiotic exposure (within the prior 8–12 weeks), health‑care‑associated diarrhea, or nosocomial diarrhea that develops more than 72 hours after hospital admission. 5

In immunocompromised patients with diarrhea, obtain an expanded panel that includes bacterial culture, viral studies, and parasitic examinations regardless of stool appearance or presence of fever. 5
For patients with AIDS and persistent diarrhea, specifically test for Cryptosporidium, Cyclospora, Cystoisospora, microsporidia, Mycobacterium avium complex, and cytomegalovirus. 5

When multiple individuals develop diarrhea after sharing a common meal or in congregate settings (e.g., nursing homes, assisted‑living facilities, daycare centers), conduct broad testing for bacterial, viral, and parasitic agents irrespective of individual symptom severity or fever. 5

Do not routinely order stool culture for uncomplicated acute watery diarrhea that lacks fever, blood, mucus, or severe symptoms, as these cases are usually viral and self‑limited. 5

Submit fresh whole stool specimens (not rectal swabs) to maximize detection of bacterial pathogens; rectal swabs have a markedly lower yield. 5
For ova‑and‑parasite evaluation in diarrhea persisting ≥14 days—especially in travelers or those with known parasitic exposure—collect three separate stool specimens on different days to achieve optimal sensitivity (approximately 60–90 %). 5

Clearly indicate clinical suspicion and relevant epidemiologic factors on the requisition form, because laboratories may not automatically test for Yersinia, non‑O157 STEC, or Vibrio without an explicit request. 5
When a multiplex molecular panel yields a positive result that requires public‑health reporting or when antimicrobial susceptibility testing could influence management, request culture of the identified organism. 5

Multiplex nucleic‑acid amplification panels detect DNA from both viable and non‑viable organisms; a positive result may represent colonization rather than active infection and therefore must be interpreted in the context of the patient’s clinical presentation and symptom severity. 5