Salmonella, Shigella, Campylobacter, and Pathogenic E. coli (Bacterial Enteritis)
Acute inflammatory diarrhea from invasive enteric bacteria; supportive care is the backbone, antibiotics reserved for severe or high-risk cases (and avoided in EHEC).
Also known as: bacterial gastroenteritis, Salmonella, Shigella, Campylobacter, EHEC, STEC, O157:H7, dysentery, food poisoning
Overview
Acute infectious enteritis caused by invasive or toxigenic gram-negative bacilli that produce inflammatory diarrhea, typically with fever, abdominal cramps, and occasionally bloody stools. The four most board-relevant pathogens are nontyphoidal Salmonella, Shigella species, Campylobacter jejuni, and pathogenic Escherichia coli — particularly enterohemorrhagic (EHEC/STEC) O157:H7.
Epidemiology
Foodborne illness causes ~48 million US cases annually (CDC). Campylobacter and Salmonella are the most frequently confirmed bacterial enteric pathogens. Outbreaks linked to undercooked poultry (Campylobacter, Salmonella), eggs and reptiles (Salmonella), ground beef and leafy greens (EHEC), and person-to-person spread in daycares and institutions (Shigella).
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Ingestion of undercooked poultry, eggs, ground beef, unpasteurized dairy, or contaminated produce
Travel to areas with poor sanitation
Daycare attendance and crowded living (Shigella)
Reptile or amphibian exposure (Salmonella)
Immunocompromise, sickle cell disease (invasive Salmonella, osteomyelitis), age <5 or >65
PPI or H2-blocker use (reduced gastric acid barrier)
Pathophysiology
Salmonella invades enterocytes and Peyer patches via type III secretion, with potential bacteremia in immunocompromised hosts and sickle cell patients (osteomyelitis). Shigella invades colonic epithelium directly via M cells and produces Shiga toxin (S. dysenteriae type 1), causing dysentery. Campylobacter invades the distal small bowel and colon, sometimes triggering molecular mimicry against gangliosides (Guillain-Barré syndrome). EHEC adheres to colonic epithelium and releases Shiga-like toxin, damaging endothelium and producing hemorrhagic colitis and hemolytic-uremic syndrome (HUS).
Clinical presentation
Symptoms
Crampy abdominal pain, fever, and diarrhea developing 1-3 days after ingestion (longer incubation for Campylobacter)
Bloody or mucoid stools (dysentery pattern) more common with Shigella, EHEC, and Campylobacter
Nausea and vomiting more prominent with Salmonella
EHEC: severe abdominal cramps with bloody diarrhea and notably low-grade or absent fever
Signs / physical exam
Diffuse abdominal tenderness without peritoneal signs
Ischemic colitis — Older adults with vascular disease, sudden abdominal pain followed by bloody diarrhea, watershed areas on imaging
Appendicitis with periappendiceal phlegmon — RLQ pain, fever, anorexia; CT distinguishes from terminal ileitis (which Yersinia and Campylobacter can mimic)
Diagnostic workup
Diagnostic criteria
Clinical syndrome of acute inflammatory diarrhea plus positive stool culture or PCR for the responsible pathogen.
Labs
Stool culture or multiplex GI PCR panel — preferred initial test; identifies Salmonella, Shigella, Campylobacter, STEC
Stool Shiga toxin assay (EIA or PCR) in any bloody diarrhea — essential to identify EHEC
CBC: leukocytosis with left shift in Shigella; falling platelets and rising creatinine raise concern for HUS
BMP for renal function and electrolytes
Blood cultures if febrile or immunocompromised (invasive Salmonella)
Imaging
Not routinely required
CT abdomen if severe pain, peritoneal signs, or toxic megacolon suspected
Treatment
First-line
Aggressive oral or IV rehydration with isotonic fluids and electrolyte replacement
Empiric antibiotics generally NOT indicated for routine community-acquired bacterial enteritis; reserve for severe disease, dysentery, immunocompromise, age extremes, or confirmed Shigella
Avoid antimotility agents (loperamide) in dysentery or suspected EHEC — increased risk of toxic megacolon and HUS
Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants.