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.

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.