Bacterial Gastroenteritis

Acute diarrheal illness from bacterial infection of the GI tract, via toxin-mediated (preformed toxin, e.g. Staphylococcus aureus, Bacillus cereus), toxigenic (in vivo toxin production, e.g. enterotoxigenic E. coli, V. cholerae), or invasive (mucosal invasion causing an inflammatory, often bloody diarrhea, e.g. Salmonella, Shigella, Campylobacter, enteroinvasive/enterohemorrhagic E. coli) mechanisms.

See the dedicated Salmonella, Shigellosis, and Cholera entries for organism-specific detail; this entry addresses the general approach.

Watery diarrhea (toxin-mediated/toxigenic) versus bloody, mucoid diarrhea with fever, cramping, and tenesmus (invasive) provides an important initial clue to likely cause and severity.

Onset timing after exposure is informative: under 6 hours suggests preformed toxin (S. aureus, B. cereus); 8 to 16 hours suggests C. perfringens; over 16 hours suggests viral, toxigenic bacterial, or invasive bacterial causes.

Most cases require no investigation and are managed empirically (see Acute Gastroenteritis entry for the general approach).

Investigation is warranted for bloody diarrhea, severe illness, immunocompromise, recent hospitalization/antibiotics, or symptoms beyond 7 days: stool culture and sensitivity, stool multiplex PCR panel where available (faster, more sensitive), and C. difficile toxin/PCR if relevant antibiotic exposure.

Rehydration is the priority regardless of cause (see Acute Gastroenteritis and Severe Dehydration entries)
Antibiotics are not routine and are reserved for specific situations: severe Shigella infection (ciprofloxacin 500 mg PO bd for 3 days, or azithromycin 500 mg PO od for 3 days), severe or prolonged Campylobacter (azithromycin 500 mg PO od for 3 days if within 3 days of symptom onset), and enteric fever-type presentations (see Salmonella and Typhoid entries)
Avoid antibiotics if enterohemorrhagic E. coli (EHEC/STEC) is suspected (bloody diarrhea with minimal/no fever, particularly in children), given the risk of precipitating hemolytic uremic syndrome through increased toxin release
Antimotility agents avoided in bloody or invasive diarrhea given risk of prolonging illness/toxic megacolon

Referral: gastroenterology/infectious disease for severe, prolonged, or complicated cases.

Clostridioides Difficile Colitis

Clostridioides difficile colitis results from toxin-producing C. difficile overgrowth following disruption of normal colonic flora, most commonly by antibiotic exposure (virtually any antibiotic, though clindamycin, fluoroquinolones, and broad-spectrum cephalosporins carry particularly high risk), causing a spectrum from mild diarrhea to life-threatening pseudomembranous colitis and toxic megacolon. A leading cause of healthcare-associated diarrhea.

Watery diarrhea (sometimes with mucus, rarely grossly bloody), abdominal cramping, fever, and leukocytosis, typically developing during or within several weeks of antibiotic exposure. Severe disease features marked leukocytosis (often above 15 x10⁹/L), significant renal impairment, hypoalbuminemia, and hypotension; fulminant disease includes toxic megacolon (colonic dilation above 6 cm with systemic toxicity), ileus, or perforation, a surgical emergency.

Stool testing: a two-step approach is standard, given neither test alone has ideal sensitivity/specificity, glutamate dehydrogenase (GDH) or PCR as a sensitive screen, followed by toxin EIA to confirm active toxin production in GDH/PCR-positive samples (PCR alone can detect toxigenic colonization without active toxin-mediated disease, risking overdiagnosis and overtreatment if used in isolation)
Testing should only be sent on unformed stool from a patient with clinically significant diarrhea, not for surveillance or in asymptomatic patients
CT abdomen for suspected fulminant disease (colonic wall thickening, dilation, pericolonic stranding); flexible sigmoidoscopy showing pseudomembranes supports diagnosis where testing is equivocal

Stop the inciting antibiotic where feasible
Non-severe disease: vancomycin 125 mg PO qds for 10 days, or fidaxomicin 200 mg PO bd for 10 days (increasingly preferred first line given lower recurrence rates, where cost/availability allow); metronidazole is now generally reserved for settings where vancomycin/fidaxomicin are unavailable, given inferior efficacy
Severe disease (WCC above 15 x10⁹/L, or creatinine 1.5x baseline): vancomycin 125 mg PO qds for 10 days (higher-dose oral vancomycin, e.g. 500 mg qds, considered in fulminant disease)
Fulminant disease (hypotension, ileus, megacolon): oral/NG vancomycin 500 mg qds PLUS IV metronidazole 500 mg tds, with vancomycin enema (500 mg in 100 mL saline PR qds) added if ileus prevents oral drug from reaching the colon; urgent surgical consultation given the risk of perforation and need for colectomy in refractory fulminant disease
First recurrence: vancomycin taper/pulse regimen, or fidaxomicin if not used initially
Multiple recurrences: fecal microbiota transplantation is highly effective and increasingly standard for recurrent disease refractory to antibiotic approaches; bezlotoxumab (a monoclonal antibody against toxin B) may be added to standard antibiotic treatment to reduce recurrence risk in high-risk patients
Infection control: contact precautions, and note alcohol-based hand sanitizer is ineffective against C. difficile spores, soap and water handwashing is required

Referral: gastroenterology for recurrent disease or FMT; surgery emergently for fulminant colitis, megacolon, or perforation.

Bacterial Gastroenteritis

Overview

Clinical Features

Diagnosis

Management

Overview

Clinical Features

Diagnosis

Management