Gastroenterology · Infectious Gastroenteritis
The facts most likely to be tested
Norovirus is the most common cause of acute gastroenteritis in all age groups and is frequently associated with outbreaks in closed settings like cruise ships and nursing homes.
Rotavirus is the most common cause of severe, dehydrating diarrhea in unvaccinated infants and young children.
Salmonella species are associated with poultry and reptile exposure and may cause reactive arthritis or osteomyelitis in patients with sickle cell disease.
Campylobacter jejuni is the most common bacterial cause of gastroenteritis, often presenting with bloody diarrhea and a strong association with Guillain-Barré syndrome.
Shigella species produce a potent Shiga toxin that can lead to febrile seizures in children and hemolytic uremic syndrome (HUS).
Enterotoxigenic E. coli (ETEC) is the most common cause of traveler's diarrhea, typically acquired from contaminated food or water in developing countries.
Oral rehydration therapy (ORT) is the first-line treatment for mild to moderate dehydration, while intravenous fluids are reserved for patients with severe dehydration or intractable vomiting.
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A 24-year-old male presents to the urgent care clinic with 3 days of watery diarrhea, abdominal cramping, and low-grade fever. He recently returned from a trip to Mexico where he consumed local street food. He reports no blood in his stool and is currently tolerating oral fluids. His physical exam is notable for mild tachycardia and dry mucous membranes, but he is otherwise hemodynamically stable.
What is the most likely etiology of this patient's condition?
Enterotoxigenic E. coli (ETEC)
The patient's presentation of traveler's diarrhea following recent international travel is classic for ETEC, which is the most common cause of this condition as outlined in the sixth bet.
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High yield triage
Etiology / Epidemiology
Viral (Norovirus) is the most common cause in adults; Rotavirus is common in unvaccinated children.
Clinical Manifestations
Acute onset of watery diarrhea, vomiting, and abdominal cramps; rice-water stools suggest Vibrio cholerae.
Diagnosis
Diagnosis is clinical; Stool culture is reserved for severe, persistent, or bloody cases.
Treatment
Oral rehydration therapy is first-line; Loperamide is used for symptomatic relief in non-bloody diarrhea.
Prognosis
Most cases are self-limiting; dehydration is the primary cause of morbidity.
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Epidemiology & Etiology
Viral pathogens account for the majority of cases, with Norovirus being the leading cause of outbreaks in all ages. Bacterial causes like Salmonella, Campylobacter, and Shigella are more common in cases of inflammatory or bloody diarrhea. Travel history, daycare attendance, and consumption of undercooked poultry or shellfish are key risk factors.
Pertinent Anatomy
The small intestine is the primary site of fluid secretion and absorption. Inflammation of the intestinal mucosa disrupts the brush border enzymes, leading to osmotic diarrhea. Severe involvement of the colon results in dysentery, characterized by frequent, small-volume, bloody stools.
Pathophysiology
Pathogens induce diarrhea via two main mechanisms: secretory (toxin-mediated, e.g., Enterotoxigenic E. coli) or inflammatory (mucosal invasion, e.g., Shigella). Toxin-mediated processes increase cyclic AMP or cyclic GMP, causing massive fluid secretion. Invasive organisms cause direct tissue damage, leading to the presence of fecal leukocytes and blood.
Clinical Manifestations
Patients present with sudden onset of diarrhea, nausea, and vomiting. Red flags include high fever, severe abdominal pain, bloody stools, and signs of hypovolemia (tachycardia, hypotension). Rice-water stools are classic for Vibrio cholerae, while pea-soup stools may be seen in Salmonella typhi.
Diagnosis
Diagnosis is primarily clinical. Stool culture is indicated only for patients with fever >101.3°F, bloody stools, or symptoms lasting >7 days. Fecal lactoferrin or fecal leukocytes are sensitive markers for inflammatory diarrhea.
Treatment
Oral rehydration therapy (ORT) is the cornerstone of management. Loperamide is a first-line antimotility agent but is contraindicated in bloody diarrhea due to the risk of toxic megacolon. Antibiotics are reserved for severe cases or specific pathogens; Azithromycin is the preferred agent for severe bacterial gastroenteritis.
Prognosis
Most patients recover within 3-5 days with supportive care. Dehydration and electrolyte imbalances (hypokalemia, metabolic acidosis) are the most common complications requiring hospitalization. Monitor for Hemolytic Uremic Syndrome (HUS) in children following E. coli O157:H7 infection.
Differential Diagnosis
Appendicitis: localized RLQ pain and peritoneal signs
Inflammatory Bowel Disease: chronic, relapsing course with weight loss
Celiac Disease: malabsorption symptoms triggered by gluten
Clostridioides difficile: history of recent antibiotic use
Giardiasis: foul-smelling, greasy stools after camping/well water