INFECTIOUS SYNDROMES

Infectious Diarrhea

Classification: Acute gastrointestinal infection producing secretory, inflammatory, cytotoxic, or systemic disease (Fiske & Bloch, 2019; Norris, 2020).

Key diagnostic discriminator: Watery high-volume diarrhea suggests secretory/noninvasive disease; fever, blood, tenesmus, and severe pain suggest invasive or cytotoxic disease. Hydration status is the first assessment (Carbo & Smetana, 2012; Seller & Symons, 2018).

Clinical priority: Severe dehydration, peritonitis, toxic megacolon, sepsis, pregnancy, very young/old age, profound immune compromise, or HUS features require urgent escalation (Carbo & Smetana, 2012; Fiske & Bloch, 2019).

Etiology and risk factors

  • Risks include contaminated food/water, travel, outbreak or sick contacts, animal exposure, antibiotics or healthcare exposure, sexual exposure, immune compromise, and age extremes (Fiske & Bloch, 2019; Norris, 2020).
  • Bacteria, viruses, and parasites cause disease through preformed toxin, enterotoxin, adherence, mucosal invasion, or cytotoxin. Incubation and exposure narrow the organism list (Fiske & Bloch, 2019; Norris, 2020).

Pathophysiology

  • Preformed toxins stimulate vomiting/diarrhea without invasion. Enterotoxins activate chloride/water secretion in small intestine, producing watery stool with limited inflammation (Fiske & Bloch, 2019; Norris, 2020).
  • Invasive or cytotoxic pathogens injure ileal/colonic epithelium, producing neutrophilic inflammation, fever, pain, and blood. Fluid and electrolyte loss can cause hypovolemia, kidney injury, and shock (Fiske & Bloch, 2019; Norris, 2020).
  • Toxin or immune-mediated sequelae include hemolytic uremic syndrome, reactive arthritis, and Guillain-Barre syndrome (Fiske & Bloch, 2019; Norris, 2020).

Clinical manifestations

  • Watery or bloody stool, abdominal cramps, nausea/vomiting, fever, urgency/tenesmus, dehydration, or systemic toxicity. Small-bowel disease often produces large-volume watery stool; colitis produces frequent small-volume inflammatory stool (Carbo & Smetana, 2012; Seller & Symons, 2018).
  • Danger findings include orthostasis, oliguria, altered mentation, severe abdominal tenderness/distention, high fever, blood, sepsis, or neurologic weakness (Carbo & Smetana, 2012; Seller & Symons, 2018).

Findings that argue against or redirect

  • A chronic course redirects toward inflammatory bowel disease, malabsorption, medication, endocrine, or functional disease, although persistent parasites and C. difficile remain possible (Carbo & Smetana, 2012; Seller & Symons, 2018).
  • Absence of fever or blood does not exclude infection. Stool leukocytes/lactoferrin/calprotectin cannot identify a specific pathogen (Carbo & Smetana, 2012; Seller & Symons, 2018).
  • Do not assume a positive multiplex result is causal without considering colonization, prolonged shedding, and clinical context (Carbo & Smetana, 2012; Seller & Symons, 2018).

Diagnostic evaluation

  • Most mild, short, uncomplicated illness needs no testing. Test stool when fever, blood/mucus, severe pain, sepsis, immunocompromise, outbreak/public-health concern, persistent course, or important exposure is present (Carbo & Smetana, 2012; Fiske & Bloch, 2019).
  • Use culture or multiplex molecular testing for bacterial pathogens; include Shiga toxin testing when STEC is possible. Test for C. difficile after relevant antibiotic/healthcare exposure and clinically significant diarrhea. Use ova/parasite or targeted antigen/PCR for persistent/travel/immunocompromised patterns (Carbo & Smetana, 2012; Fiske & Bloch, 2019).
  • Assess electrolytes, renal function, CBC, lactate, and blood cultures when dehydration, HUS, or sepsis is possible (Carbo & Smetana, 2012; Fiske & Bloch, 2019).

Expected diagnostic and laboratory findings

  • Secretory/noninflammatory: watery stool, limited fecal inflammatory evidence, often no gross blood. Inflammatory: blood, fecal leukocyte markers, fever, and colonic symptoms (Carbo & Smetana, 2012; Fiske & Bloch, 2019).
  • Definitive etiology requires compatible organism/toxin detection. STEC concern rises with bloody diarrhea and abdominal pain, sometimes with little fever; falling hemoglobin/platelets and rising creatinine indicate HUS (Carbo & Smetana, 2012; Fiske & Bloch, 2019).
  • C. difficile diagnosis requires compatible diarrhea plus toxin or toxigenic-organism testing interpreted through the local algorithm (Carbo & Smetana, 2012; Fiske & Bloch, 2019).

Differential diagnosis

  • Inflammatory bowel disease: chronic/recurrent symptoms, weight loss, extraintestinal findings, endoscopic/histologic inflammation without an explanatory pathogen (Carbo & Smetana, 2012; Seller & Symons, 2018).
  • Ischemic colitis: abrupt pain and hematochezia in a vascular-risk patient; CT/endoscopy pattern (Carbo & Smetana, 2012; Seller & Symons, 2018).
  • Medication/osmotic diarrhea: temporal exposure and improvement with withdrawal/fasting pattern (Carbo & Smetana, 2012; Seller & Symons, 2018).
  • Irritable bowel syndrome: chronic pain related to defecation without fever, bleeding, dehydration, nocturnal symptoms, or inflammatory abnormalities (Carbo & Smetana, 2012; Seller & Symons, 2018).

Treatment and management

  • Oral rehydration is preferred when feasible; use intravenous isotonic fluid and electrolyte/glucose correction for severe dehydration, shock, or inability to drink (Fiske & Bloch, 2019; Norris, 2020).
  • Use antimicrobial therapy selectively according to pathogen, severity, host, and public-health guidance. Avoid antibiotics and antimotility agents when Shiga toxin-producing E. coli is suspected because of HUS risk (Fiske & Bloch, 2019; Norris, 2020).
  • Use contact precautions and soap-and-water hand hygiene for suspected C. difficile; manage outbreaks and reportable disease with infection prevention/public health (Fiske & Bloch, 2019; Norris, 2020).

Additional complications and red flags

  • New weakness or areflexia after diarrhea may indicate Guillain-Barre syndrome (Carbo & Smetana, 2012; Fiske & Bloch, 2019).

Content last reviewed:

References

Carbo, A. R., & Smetana, G. W. (2012). Diarrhea. In M. C. Henderson, L. M. Tierney, Jr., & G. W. Smetana (Eds.), The patient history: An evidence-based approach to differential diagnosis (2nd ed.). McGraw-Hill.

Fiske, C. T., & Bloch, K. C. (2019). Infectious diseases. In G. D. Hammer & S. J. McPhee (Eds.), Pathophysiology of disease: An introduction to clinical medicine (8th ed.). McGraw-Hill Education.

Norris, T. L. (2020). Porth’s essentials of pathophysiology (5th ed.). Wolters Kluwer.

Seller, R. H., & Symons, A. B. (2018). Differential diagnosis of common complaints (7th ed.). Elsevier.