Infectious Disease · Gastrointestinal Infections
The facts most likely to be tested
Shigellosis is characterized by bloody diarrhea, fever, and abdominal cramps caused by the Shiga toxin which inhibits the 60S ribosomal subunit.
The pathogen is transmitted via the fecal-oral route and has an extremely low infectious dose, requiring as few as 10 to 100 organisms to cause disease.
Stool studies typically reveal fecal leukocytes and erythrocytes on microscopy, confirming an inflammatory/invasive etiology.
Seizures are a classic, though rare, neurologic complication in children, often occurring in the absence of severe electrolyte disturbances.
Hemolytic Uremic Syndrome (HUS) is a serious potential complication, characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury.
Ciprofloxacin or Azithromycin are the preferred antibiotic treatments to shorten the duration of illness and reduce the period of fecal shedding.
Antimotility agents like loperamide are strictly contraindicated as they can worsen the clinical course by prolonging toxin exposure to the intestinal mucosa.
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A 6-year-old boy is brought to the urgent care clinic with a 2-day history of high-grade fever and frequent, small-volume stools containing bright red blood and mucus. The patient reports severe tenesmus and lower abdominal pain. Physical examination reveals diffuse abdominal tenderness and hyperactive bowel sounds. A stool sample is sent for culture, and microscopy shows numerous polymorphonuclear leukocytes. The patient is currently hemodynamically stable.
Which of the following medications is most appropriate to initiate in this patient?
Azithromycin
The patient presents with classic symptoms of shigellosis (dysentery); antibiotic therapy is indicated to reduce the duration of symptoms and fecal shedding, with azithromycin being a first-line choice in pediatric patients.
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Etiology / Epidemiology
Highly contagious gram-negative bacteria transmitted via fecal-oral route; common in daycare centers and crowded settings.
Clinical Manifestations
Presents with dysentery: bloody, mucoid diarrhea, high fever, and tenesmus.
Diagnosis
Gold standard is stool culture; clinical diagnosis often supported by fecal leukocytes.
Treatment
First-line is ciprofloxacin; avoid antimotility agents due to risk of toxic megacolon.
Prognosis
Self-limiting, but watch for hemolytic uremic syndrome (HUS) in pediatric patients.
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Epidemiology & Etiology
Caused by *Shigella* species, most commonly *S. sonnei* in the US. It has a very low infectious dose (<100 organisms), facilitating rapid spread in schools and nursing homes. Transmission occurs via contaminated water, food, or direct person-to-person contact.
Pertinent Anatomy
The pathogen primarily invades the colonic mucosa, specifically targeting the M cells in Peyer's patches. This localized invasion leads to intense inflammation and ulceration of the large intestine.
Pathophysiology
The bacteria invade the intestinal epithelium and escape the phagosome to replicate in the cytoplasm. It produces the Shiga toxin, which inhibits protein synthesis by targeting the 60S ribosomal subunit. This results in mucosal cell death, leading to the classic dysentery presentation.
Clinical Manifestations
Patients present with sudden onset of high fever, abdominal cramps, and bloody, mucoid stools. Tenesmus—a painful, ineffective urge to defecate—is a hallmark symptom. Red flags include signs of dehydration, altered mental status, or toxic megacolon.
Diagnosis
The stool culture is the gold standard for definitive identification. Microscopic examination of stool typically reveals fecal leukocytes and erythrocytes. A complete blood count may show a leukemoid reaction.
Treatment
Fluid and electrolyte replacement is the cornerstone of therapy. Ciprofloxacin is the first-line antibiotic for severe cases or to shorten the carrier state. Antimotility agents (e.g., loperamide) are strictly contraindicated as they increase the risk of toxic megacolon.
Prognosis
Most cases resolve within 5–7 days. Hemolytic uremic syndrome (HUS) is a rare but serious complication, characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Monitor for decreased urine output and pallor.
Differential Diagnosis
Salmonellosis: usually associated with poultry/reptiles and pea-soup diarrhea
Campylobacter: often follows raw poultry ingestion; associated with Guillain-Barré
EHEC: bloody diarrhea without fever; associated with undercooked ground beef
Entamoeba histolytica: parasitic infection; often presents with liver abscess
Yersinia enterocolitica: mimics acute appendicitis due to mesenteric adenitis